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Could you post some more info:
How are you calculating 10 to 10.5:1 compression?
What pistons? flat tops, or stepped for quench?
What mods have been done to the heads?
What size tires to help figure cruse RPM?
What vehicle or vehicle weight?
What performance goals?
How low of octane fuel is going to be used?
What altitude will the vehicle be driven?
How often will it be driven?
Does the cam have to work with stock stamped rocker arms?
If aftermarket rocker arms, what ratio?

From your initial post it looks like the car is setup for street driving. The gear/converter/intake/carb seem to be OK for a mild performance, but the compression might be an issue. At least it is on the high side. It is easier to remove some chamber volume or piston material or use a thicker head gasket to lower compression then to add material or reduce gasket thickness to increase compression.
Most off the shelf cams usually expect less compression with a better intake system. You might want to call a cam grinder and see if they recommend a custom ground cam with extra intake duration and a wider LSA, or change the installed centerline to retard the cam?



I was just going off what these engines supposedly had from the factory?
The engine builder said he would just use some 340 replacement pistons?
Nothing done to the heads just stock J heads with 2.02 1.60 valves

Not sure on tires size maybe 245 ?
Its in a 72 challenger
Its a nicely restored car that will get driven to some car shows etc, may never see the track?
Most I can get is 91 octane
DA is around 2-3000 feet most the time?
will have the stock shaft system still in place

hope this helps