I've got a used but good 383 shortblock and OEM heads, both have been rebuilt at some point in time by people I bought them from so I don't have any details on the machine work completed. They are going into my turbocharged Fury as a small upgrade.
Do I need to be concerned about the surface smoothness to use Cometics - I don't know what the machining was finished at on either. Was running 12psi on the smog engine, looking to be in the same range on this one as well (retaining water/meth injection installed in the car).
Current engine is a smog deal with 8.5:1 CR with .020 gaskets that lived just fine. New engine is going to be around 9-9.25:1 if I use the C5461-040 gaskets I already own.

Thanks!

Cometics need a 50RA or smoother finish on the heads and block to seal properly per Cometics instructions. 50 RA is pretty smooth, almost as smooth as glass
When in doubt, due without when it comes to parts your not sure of

so 50RA would not be a 'typical' prep by a machine shop? Without that prep, am I better off with the normal felpro?

as cab said, 50RA is almost like glass.
i have a GAR pocket profile surface comparator we used at work to quickly check surface finish on the shop floor.
it jumps from 32RA to 63RA, and 63RA is almost like glass as well, so you can just imagine what a 32RA finish is like ! [not to mention the lowest on the tool, which is 2RA ! ]
i tried to take a picture of this tool, but my camera just made it look like a super polished piece of material.
this pocket tool also has different RA finishes, depending if the surface was :

honed, lapped or polished
ground with the periphery of the wheel
ground with the flat side of the wheel [blanchard]
shaped or turned
side/end milled or profiled
or milled with the periphery of the cutter.

pretty neat pocket tool, all things considered, to check against the machined deck or head surface.

and the typical machine shop "rebuilder" finish is not 50RA. sorry.

I tried to look for tools quick, it looked like the cheapest might have been $500, was I looking at the right things?

i can't answer that, as i was supplied this tool at work over 35 years ago.
it's just a 2"x4" [approximate measurements] piece of material with the profiles [examples] being approximately 1/2" square. it has a leather like pouch it is stored in.
do you have a link to what you were looking at ?

something like this, which is different than what you describe

https://www.abqindustrial.net/store...KbY0fPOqRLapYIA5rgozwEiez_kaAkF9EALw_wcB

Not in my world! Technically its 50 microinches RA. In my world 50 microinches RA is only somewhat smooth, but its all relative to what you are doing. Sleeve (babbitt) bearings generally want a 16 - 32 microinches RA finish. 16 is getting pretty smooth.

I used some Cometics on my 383 w/ Edelbrock heads when I had the engine apart to gap the rings for a turbo. I did not do anything other than clean the surfaces for prep. I sprayed the gaskets with some copper spray and put em on. So far it has held 7psi of boost (with a plan to go to 12psi).

I am not an experienced engine builder, but I hope this info helps

MLS gaskets are made with thin sandwich of stainless steel, stainless is very tough but is so hard it will not conform to any irregularities, hence the need for a 50ra surface finish. Back in the day we used single layer steel gaskets coated with aluminum paint, or cooper coat, the paint and copper coat was there to fill small surface irregularities. The best old school gaskets are copper, copper is soft and conforms, and then with heat, work hardens and gets tough. I believe top fuel still uses them, so since money for gaskets is not an issue, they must be good right? composition gaskets like say a fel pro seal great, but may give it up over time, ask any mechanic working on cars in the 80's and 90's how many head gaskets they installed. Most of which failed just about the 150,000 mile mark. They helped me raise my family.
My experience is that for a normally aspirated engine, if you don't have the correct surface finish for MLR gaskets, a composition gasket works fine, used many of them up to 14 to 1 compression, and never had an issue. The only engines I have ever had a problem with head gaskets on a performance engine were the ones that only have four bolts per cylinder, like a 340 LA for example, they get a copper gasket with a o-ring in the block, with high compression. The guys that hop up diesel's what do they use? they dump the MLR gasket and use a copper gasket with a fire ring installed. At least the truck pullers around here do.
Gasket companies went to MLR gaskets because of issues with OEM engines, 20 years ago, so that is the technology they are using, which may or may not be what you need with an older performance muscle car engine.

Not particularly scientific I know, but the "Fingernail trick" would probably answer your surface roughness question. If the surface catches your finger as you drag your finger over the surface, it's too rough for a MLS gasket.

I appreciate the inputs, sounds like traditional felpro is a better choice for me.

Researching other options based on y'alls input, what about Felpro's permatorque MLS that's good to 80Ra, anyone have experience with those vs the traditional 1009 gasket?

The 1009 bore size was originally design for the 426 and 383 4.250 bore size so they are marginal to no good on 440 and 400 blocks bored over size
I've used a bunch of them with no problems on the deck sealing with out the receiver grooves they, Fel Pro, recommend when using them

If you can find the felpro mls, and your surfaces are decent/not pitted or scratched, you’ll be fine.
I honestly think you would be fine with a felpro composition gasket. I strongly recommend studs. I used composition gaskets on mine with iron heads. At around 20 pounds of boost they would leave evidence of combustion lines on my firewall and back of the alternator, but never actually failed. Went with copper/ o ring when I switched to aluminum heads.
Caution with iron heads on a turbo b engine... the extreme heat swings will likely crack the cylinder heads externally in a horizontal line Just below the two center exhaust ports. If you suddenly develop coolant leaks, this is a likely source.