Anyone building up a GMC engine,especially a 302, must become an expert on all the early GMC inlines. You have to know what parts are interchangable and be creative about moving parts from one size engine to the another to get the setup that you want.
As far as performance parts, I agree that there is a VERY small group of people that sell the performance parts and if performance is your goal you need to accept this fact and be ready to pay their prices.
If a reliable stock engine is your goal, your local parts house has many of the parts(internal stuff i.e. lifters, seals, gaskets etc...)you need. If the college punk at the local parts counter can't find the 302 engine in the catalogs, try telling him you have a 270 in your '57 GMC 1/2 ton P/U. The parts such as seals and gaskets will all be the same and the parts dude will be able to find the 270 easier because he was looking in the light Duty truck book to begin with. Parts people seem to relate better to 1/2 ton stuff better than the Heavy Duty vehicles for some reason.
When you are at the auto parts store you will need to ask for some things by vehicle application and some things by engine application. Example: If you are putting a 302 in a 47-54 GMC p/u don't go in and ask for the radiator hoses for 302 because the hoses you get will be for the 2-1/2 ton truck and because the radiator was farther away from the engine in these trucks, your hoses will be WAY to long. Just tell the punk at the counter you have a '52 1/2 ton P/U with a 228. The water pump is the same(pulley width being the only difference) on all 228,236,248,256,270, and 302 engines so the determining factor is what size truck the engine is pulling around.
Don't forget Uncle Sam. In 1952 thousands of GMC 6x6 2-1/2 ton trucks were built. Many of them now sit in junk yards across the country. Each one had a GMC 302 andthe 6x6 trucks before '52 had the 270. Now..... I know that alot of the external stuff is different but lets say you needed a camshaft, head, crankshaft, connecting rods etc. for your 270 or your 302, your all set. Heck, even the military block will work with a few easy modifications.
There are several companys that specialize in GMC 6x6 trucks and will sell you all the parts you need for your 302 and a lot of it is NOS military surplus. Memphis Equipment Company is one in Tennessee-not to far for those in Georgia
Phone: 901-774-0600 (they even have a website)
Three more words: eBay, eBay, eBay.
Lots of people are selling surplus inventories and the deals are good. Email the sellers who look like they are selling NOS surplus parts and ask if they have the parts you need(the same simple way as you did with the guy at the auto parts store). You will get lots of negative replys, but the one time you find the parts you need will make it all worthwhile. Buy old parts manuals so that you can tell if the part number in the auction description will work for your application. You must assume certain things to get what you want also. Lets say a guy has a crankshaft pulley dampener up for auction and and after looking up the part number that he gave you in your '55 GMC parts manual, you determine that it is for a 248 engine. Will it work on a 302? Of course!! Because you are the savy GMC expert and you know that all the crankshafts have the same diameter on the front. GMC was a master at interchangability!!!!!
Building any inline is going to cost money but you can make it cost less by using available resources and being savy. Some will find that the thrill of the chase makes it all the more fun.
Hope this helps all those out there on "the hunt".
