Stock pistons still work well....one of the simplest things to do is source oversize rings and properly gap them to spec for a stock piston as the factory stock rings are notoriously undersized...more power immediately. No billet rods/flywheels out there. David Wulf has made me shorty headers for my collection of big blocks. Not much of a power gain, just look good. You've got massive valves in the big block, so either NOS valves if the valve face is worn or simply clean up and lap. If you've got pinned valve retainers, get rid of those valves and go to valves with traditional spring retainers (slop in the valve over time causes a groove in the valve face). Plenty of carb options as Delray notes but a China knock off works fine. Pure gas is the best option for these engines (Southern States sells it).
Replacing the rod with a new one is a good idea. Clean all the casting flash off the rod and make sure you have an oiler hole to the main bearing journal--I do mine at 1/16" and I chamfer the hole on the journal side and polish the bearing surface after chamfering. That's the weak point of this engine.
For points engines: Timing, timing, timing. Make sure you have point gap set properly and adjust timing on compression stroke. For this engine, being a little off means hard starting if it'll start at all.
Remember this engine was not intended for high rpm as it's designed for torque. Gearing will make a huge speed impact on the bike. My H60 on a Gilson frame with clutch (geared at 5.5:1) flat rips up to speed and could be geared as low as 5:1 and still pull strongly. My Gilson H60 bikes with TAV can climb trees at half throttle and still go well over 40 mph wide open.