for my truck with a hybrid LA/Magnum 318. I have Hooker Super Comps, an LA shortblock and EQ Magnum heads. I had to get 2 sets of manifold gaskets to get them to seal before I put the headers on (too big towards the bottom side of the port, holes in the gasket were too "tall", 1st set)
Ran into same problem with the 1st header gaskets I got (at least I matchjed them up before actually installing them so i was able to return them) These were FelPros; I have Mr Gaskets (Not Ultra Seals though) #358 and they fit fine, but I ain't replacing header gaskets every 1500 miles!!
Got 2 sets of the MrGasket 358s at a local swap for $8/set; and already the pass side is blown. Headers were brand new,never previously installed, before I put them onto my truck; but at least 20 years old swap meet finds.
So what header gaskets do I need that will(1) match the ports and (2) LAST? The LA headers matched the EQ ports actually pretty nicely.

Flatout Gaskets
http://www.flatoutgroup.com/gaskets/2007OnlineCatalogPriceGuide.asp

7026 CHRYS SB 273-360CI GRAPHITE Header Gaskets Port 1.27"x1.80".(2) $28.40

7026C CHRYS SB 273-360CI RCC COPPER Header Gaskets Port 1.27"x1.80".(2) $53.28

7026S CHRYS SB 273-360CI STEELCLAD/GRAPHITE Header Gaskets Port 1.27"x1.80".(2) $42.04

pricey but these should last

i use the copper seal gaskets on my truck. have had headers on and off many times and still got same gaskets. they are tuff as heck and dont leak

I use a little permatex copper on my header gaskets

let it cure over night,have not had a leak in 2 yrs now

welds at the collector is another story though! right out the box

I got the headers with the new ball and cone to get rid of the collector gasket also

it helps to have the exhast hung correctly to allowing for engine torque,IMO

had to re-hang mine cause it was to solid and the 2 pipes were welded together at the muffs with cross braces and hung on the stock ridged muff hanger that cam on the single exhast,( both pipes down one side)

would not let it move and was blowing gaskets and riping the thin lip of the collector flange off the ends

now the header hangs on the engine and the pipes muffs and tail pipes hang from 2 swivel mount just past the rear axle to let it twist some whith out pulling it apart at the gaskets
(removed the saddle gas tank from one side and run them down both side straight back)

I also moved the muffs as close to the header as I could to help hang more weight toward the headers instead of the tail pipes

fixed the probs I had with it blowing the header gasket at the head

so headers and 2 hangers past the rear axle is all I have hanging it now

Check the header flange faces and see if you have a bad weld on one of the tubes. I had a similar problem and finally just pulled the headers to look real close at them. Found one of the welds had a high spot that was causing the flange not to seal fully and blowing out the gaskets. Once I ground it down I could run 1 set of gaskets with no leaks and no problems.

Header flange trueness is most important and most better gaskets can be used. The thinner the flange thickness, the more warpage under heat, resulting in leakage. Had hooker comps on the Dart and always had leaks. I had to split/cut/separate the flanges to get a better seal.

You are using LA exhaust gaskets on Magnum heads. "Gibson" # 9245 is the correct exhaust header gasket for magnum heads. Great fit - no leaks. Ether Summit or Jegs sells them.

remflex.com

Remflex is the only way to go.

www.remflex.com

I just put a set on a slant six with headers, fit perfectly NO LEAKS.

Scott

they fixed a warped flange problem I had - great product

I use that material in gaskets in the commercial piping industry - Glad they took it to the car scene

Post deleted by Rollin Hand

I run copper headder gaskets with Permatex super copper as a sealing aid on both sides and never a problem.

I believe that they can be reused, I seem to recall someone on the slant six board saying he reused thme many times. They are at least 1/8 inch thick and made of a graphite material. I used them at the manifold and the collector.

Believe it or not, take a look on amazon.com occassionally they come up on sale there with free shipping.
scott