I wonder if the heads were flowed with the intake manifold attached.
I have seen where this can change the lift point and severity of the flow numbers backing up.

Also, testing at a higher pressure can also be revealing.

We all have our own way of doing things, but I think I'd just try and make it so the heads didn't drop off quite as bad, and run a more traditional cam.

Also, the flat tappet dwell cam option would obviously be a way cheaper approach to at least "test the theory".

Looking through some notes.....
1970 T/A head, 2.02 valve w-11/32 stem.
Basic full port and polish, remove pushrod bulge.
Full disclosure, I didn't port these heads, they had been done previously to me reworking this engine combo.
After I freshened the valve job:

Average for cyls #1 & #2

Lift---IN flow
.100---66.0
.200--135.9
.300--201.0
.400--237.7
.450--251.7
.500--258.5
.550--252.5
.600--249.8
.650--249.5
.700--249.5

I used a cam with about .625 lift with those heads.

Not a fair comparison, as the X head has a better short turn.
This one used an 11/32 stem 2.055 valve.
Basic full port and polish, no holes in port other than v/c bolt hole.

Lift----IN flow
.100---65.4
.200--128.1
.300--187.8
.400--234.3
.450--257.7
.500--272.9
.550--276.7
.600--272.1
.650--270.3
.700--270.3

maybe my valve job is shot..but these things fall off the face of the earth at .500

i am running a aftermarket stock type 2.02 valve.

thanks for the numbers Dwane

i ported these my self. the last time i touched them was 2004
but the motor ran. but its been sitting for yrs i only run the car 1-2 times the last 10yrs as my kids have been graduating and off to college now so i want to get back out there.
i noticed a couple of broken valve springs..so i pulled the heads..
for new springs... i have a few sets of roller lifters. so that led to a new cam..
i played with the cam design on my cam builder program.. and had the numbers in my engine note book. Its the last iteration in the concept of this motor...
i just wanted to put the top end back on and run the car..
i have another engine 4.060 with a 3.80"stroke crank and a set of commando heads. but i need a bunch to wrap that motor up..but i digress.

So i spent the last few months thinking i had the source to get this cam core and have it ground ... then it all fell apart when the callies cam showed up to the grinder and he said the only way he can get my numbers is to grind,treat then regrind this core.
I really want to try a roller...
(i have a few.. i have a 610" solid roller for the new motor..
and a .585 solid roller but they are just too big..)

i really want to complete this thought and do a roller in it..just ramp the valve to max flow lift ... hold it there as long as possible.
over simplified..but with a roller you can do alot more..(i still have to have split cam lobes cause i have 1.6 intake rockers and 1.5 exhaust. so a shelf cam wont work.

i suppose i could just dig out the grinding tools and try to get the heads to flow past .500" but i dont want to screw up the low lifts or go backwards. this thing could turn into a can of worms fast.. i want to keep it simple and just get the cam.

Dwayne I,Y,O how much does a valve job factor into this thing?
where do you find the valve seat angles help flow.. lower lifts or higher lifts.
my valves sit nice and high on the seat.. they look good but they where done 15yrs ago ..
maybe 100 passes or less on them.

No...not really.
the pistons are for these open chamber heads..closed chamber wont work with these pistions (hense new motor on stand)
the rocker gear is specific for these heads..(offset intake rocker and the spacing and clearance are all set up.)
the cheapest way to keep this motor is new roller springs and a new cam...fwiw

i am afraid to do more porting on the heads as i would hate to go backwards..fwiw.
but if i could find a simple solution to getting the .500" flow numbers from falling off. id consider this.

I can't say for sure in your case, but I doubt the valve job would cure the high lift flow situation.
And it's very likely you could end up with a can of worms if you start grinding more out of those heads(he said without ever seeing them).

Have you contacted LSM about making you a core?
If you waited until they were filling an order for sb mopar cores, maybe it wouldn't cost that much to have one done with lobe lift, duration, lsa that would work for you.

Frankly, I'd never spend the $$$ for an experiential custom core for something that didn't absolutely require it.

I still say the stocker flat tappet dwell lobes would work well enough to answer your question, and that wouldn't cost any more than a "normal" flat tappet cam(and you could have it in about 10 days).

i probably wouldnt do much if any grinding.. id be adding epoxy.
but i dont have my own flow bench and my flow guy is pretty busy..
it would have to go on and off the thing a bunch in between.

Since you don't seem put off at the idea of more head work, maybe these will give you some slight motivation.....

This was a set of J heads that someone had just done a very mild bowl blend on.
The intake valve was an aftermarket 2.02, 3/8 stem, but still tulip shaped.....almost as much as the OE valve(I've had better results with the Manley or Milodon pieces myself).

I went in and opened the bowl a little more, trimmed the guide boss, and slightly opened and smoothed over the pushrod bulge, and layed back the short turn some.
This was a really low cost deal, so there was no polishing after the reshaping.

Same port before(A) and after(B)

Lift--------A/B
.100---63.0/63.6
.200--124.4/128.1
.300--178.1/185.9
.400--217.3/224.9
.450--224.9/236.2
.500--215.4/248.3
.550--213.5/253.2
.600--211.7/249.4
.650--209.7/246.4

Also, fwiw, especially since getting the high lift to come around would make more sense for readily available cams....... I would happily give up 20cfm off your .400 number if I could add it to the .500 and up numbers.