1972 Demon 340 engine mods

The low compression 340 pistons will have 4 valve reliefs similar to these:
http://www.forabodiesonly.com/mopar/attachments/340-duster-jpg.1714559471/

Also, run compression tests and see what the cranking compression is. That will also give some indication of the pistons.

I really enjoyed your video. Where is that road course? Is this the type of driving for which this car will be used?

I agree on the 318; a new build would be the best way to optimize performance. You could increase the compression ratio and then go bigger on the cam without killing the low RPM torque. My son and I built his 340 with 10:1 static compression, a 268 cam, 1.6 ratio rockers and lift at .500" and Edelbrock heads and Performer intake for good high RPM breathing. Dynamic compression ratio is about 8.2. It has torque at 2000 RPM that will spin tires at 1/2 throttle. We could have gone bigger on the cam but wanted to maintain some fuel economy. We live in the eastern mountains and the type of driving that you showed on your video is exactly what we do around here.