your casting number 3884520 (from behind the drivers side cyliner head on the block) could be either a 283 or a 327 block, I didn't take too much time to look up the numbers however here is my 2cents. hope this helps!
You could spend more time researching every casting number on your block, just google the numbers & read, read, read... however for quick reference if you look at the front (crank) balancer the 283 typically used a very thin, smaller ballancer that had some holes in it. A 327 ballancer was larger, very similar to a 70's 350 ballancer (over 1" thick, solid with & no holes). Early GM blocks (yours) were typically 2 bolt main blocks & had small journal main bearings (not compatible with later model "large journal" cranks/connecting rods) but are still a very desirable blocks as they produced excellent horsepower. The 327 was a high revving block and made awesome hp due to a short stroke allowing it to rev faster.
A number of cylinder heads were available for these engines, most popular being the general car or truck cylinder heads but some cars, trucks had "double hump" cylinder heads (a double hump was cast into the end of each cylinder head) which generally had a 492 or 261 casting number and no "assessory holes", these had better flow (either 1.94 or 2.02 intake valves) and made more horsepower.
All chevrolet small blocks are very interchangable for parts, all intakes, carbs, valve covers, heads, oil pumps, etc. are interchangable, the only thing different was the cranks, rods & pistons. (until later years when chevrolet introduced "large Journal bearings" (70's) & "Vortec cylinder heads/intake" (90's)
I agree with you, my advice would be to run the engine until it blows (it may never) upgrade the usual parts(intake, carb, gaskets, etc.) to make a little extra horsepower, reliability and it will do you well for years. eventually some day you can tear it down & rebuild it!
Leyland
