i have a 1984 fleetwood hearse with a 368. i think it has the v864 system as well. i was trying to find out if there were any quick, relativly cheap performance upgrades i could do to try to squeeze as much horse power out of this motor as possible. was also wondering if any of the parts from a 472 or a 500 would interchange.

The 425/472/500 are the same family, pretty much a bolt in for a 368. Bruce Roe

I would find a 472 or 500 and bolt it in with only a few small mods ...some needed bolt on parts can be found on a 77-79 full size caddy.. If your looking for more power out of that 368, your just not going to get much... almost not worth it...

Not knowing your thoughts on performance persuit, the first thing to do would be ensure that your engine is in good tune. Good plugs, proper tuning, everything under the distributor cap in good condition, All vacuum motors working and holding required vacuum. Check those vacuum hoses for cracks. Timing set properly? Is there any hissing in the interior? These engines have vacuum controls everywhere, and a loss in vacuum causes performance loss. Keep in mind that this engine was not engineered with performance in mind.
If your considering an engine swap, keep the 425 in mind. It's lighter than the two bigger sisters, but still plenty torquey.