I have my 416 stroker bottom assembly 9.5 to 1 dish pistons at 65cc and I already have a set of J heads small valves 72cc brings my combo to 9.1 to 1 compression. These Js are they to small? , I have a set of magnums also id#5300 6671 was wondering if the magnums would be a better route for my car? 72 Cuda w/727 3000 stall Street car and I have an ld340 already w/a demonsizzler thermoquad.What should i do.Are there any problems running these magnums on my 71 340 block? Thanks Any help appreciated

You have to convert to push rod oiling but other then that they are a good choice because of the closed chamber design. With a magnum head you can run more compression and be resistant to detonation. It would be best to get them ported to feed the extra cubic inches.

Push rod oiling

The old LA heads oil the top end through passages in the block/heads where as magnum heads oil the top end through the push rods. You can read more about the conversion to magnum heads here:

http://www.moparts.org/Tech/Archive/smallblock/7.html