340 upgrades.

As has been pointed out before, the 'J' castings for '72 had the 1.880 intake valves. If you have the 'X' castings...you would indeed have the 2.020 valves. I ran a set of those on my '72 Duster 340. All factory stock when I bought it. I changed over to a set of the 'X' heads and it ran great. If you do pull the heads do a 'bowl' port on them, mill .030, freshen up the seats, replace the seals and back cut the valves 30 degrees, inexpensive mod and worth it. You already have some good spring recommendations. Comp XE 262, or XE268 will work good as will a set of headers if that is in your budget. 3.91's , TQ and TQ manifold or the Air Gap with a Holley Vacuum sec. will work well also. Would be a good street performer with good street manners. Good luck and keep us informed as to your progress and results. Terry.