Well for one thing, to get that kind of compression you would need custom built pistons which are not cheap! Wisco makes some and there is one other company that does. You need deep pockets for them. Even the 502 Chevy big glock pistons are just .010 shy of the 4.562 coffee can size bore you have. However if you can get .020 or .030 over size pistons for a 502 and then they would fit the bore and give you roughly 9.25 with some milling of the head and decking the block. I would keep it under 9.0:1. If the wrist pins and connecting rods fit then you would have a high performance engine. You would have to check it out first. It would be cheaper than custom pistons. Those ole' V6s were made for pulling and not high rpms. Cheap jap engines don't pull well but rev high. Thats why they come with 4.10 or 4.30 gears to make them pull somewhat. Those GMC engines were rugged made though. Last for many years taken care of. Personally I would build it stock and do the two things you suggested, decking and shaving the head, and have it balanced with some porting and polishing. You may have to fabricate a 4 bbl manifold for it. It there is room you might be able to bore the two back holes in it for the carb. Twin 2 1/2 or 3 inch Magnaflow exhaust would also help out the performance. I have 3 inch Magnaflow on my truck with the long muffler and it sounds great and not too noisy. Has a deep sound. Also you might get some custom headers made. Justr a thought on that. Too high of compression and you would have to run racing fuel in it. At about $7.00 a gallon I think that would not be a good idea. If you go from 7.5 to 8.5 or even 8.75 you will like it a bunch. Your mileage will increase as well. Add MSD ignition, K&N air filter and synthetic oil such as Texas Refinery Moly Pro Spec III like I use. Or Amsoil 10-30. It is doubtful that roller rockers are available unless they interchange with a known GMC or Chevy engine. If so, you want stainless steel, NOT aluminum. With the expensive cheaply made gas you relly don't want high compression. You want high torque which is what they were made for. Remember, HP wins brags and torque wins drags! Also check out
www.doubleyourmiles.com. I have one for mine once I get it set up. Every little bit helps. I wish you well on your venture.
