1972 Demon 340 engine mods

Are those aluminum heads?
Aluminum heads pull a ton of heat out of the chambers. You have to compensate for that, just to break even. You HAVE to either; A) up the static compression, or B) close the intake sooner, just to maintain the EFFECTIVE cylinder pressure. Failing to do that makes the bottom go soft. The good thing is that Aluminum heads allow very high Scr/Dcrs on even crap gas.
By the time you add up the costs of all the bolt-ons, you would be waaaaaaaaaaaaay ahead of the game, if you just brought up the compression in the first place. When that big-cammed, low compression engine falls off the pipe, your man is gonna be one unhappy customer. Nothing is worse than having to pull a shift due to running outta revs,and then having to fight your way back up the power curve. Well, almost nothing.
About your RON fuel
The best I have been able to figure out is that your RON gas is just a different way of measuring the same old gas we have here. When all is said and done, your three grades of gas are the same as our three grades of gas, as far as the anti-knock is concerned. Whatever will run here on our midgrade will run equally on your midgrade. That is the best I have been able to figure out. I COULD BE WRONG!!
SO
that means, with the aluminum heads, you can pump the crap out of your compression and run any cam you want to. Well within reason. But...... the cam has to make a wide enough powerband to work with your trans, and you have to put a rear-end behind the whole works, that puts the power at the speed you want to be at, in the gear you want to be in.
Otherwise your man is going home with a long face.
Or you can just stroke it, and leave whatever trans and gears are in there, in there,lol.
But if you run skinny 14/15 pizza cutters, just stay home.

But if he just wants to have a little fun, well that is usually a short-lived fuse. You run the course a time or two and then you are hooked.
But to all those guys that said to just throw some gears at it; with a small engine,there is zero comparison to having the right gear,at the right time,all the time. This is why we have small engines today with lotsa gears and VVT, doing what engines twice as big used to do. Power ain't everything, when it comes to just having a little fun.

But I just gotta ask; your customer doesn't seem to be hard-up for cash. And from outside the engine, you cannot tell the cubic inches nor the compression ratio. So my recommendation is just stroke it,and with aluminum heads, and with any old street cam and lots and lots and lots of cylinder pressure. I run 185psi on the lowest grade gas we have out here, namely (R +M)/2 =87E10.To keep the chamber temp up, I run the engine at 205*F. And to keep the exhaust temp down, I run dual 3 inch, full length,mandrel bent, pipes. And to keep the intake air temp down, I run fresh cold air into the 750DP/ AirGap. And to keep the underhood temps down, I ventilated it.
367 cubes was plenty for me;4.04x 3.58
Jeepers I was only gonna say a few words,lol.