'71 F350 engine ID needed

HI! I recently bought a '71 F350 1 ton with a built V8 of unknown origin. I'm thinking it's a 390 'cause she really moves out. Unfortunately, after suddenly experiencing cloud producing blowby and pulling the heads & pistons I found one piston with a hole in the side where the ring grooves are (were). The motor appears recently rebuilt probably by a machine shop, has lots of upgrades. The pistons are maked 030 on top, have full floating pins on Ford con rods, are marked 8173 on inside of skirts. Engine block is marked with 91 over 352 on front under drivers side cylinder head. Can someone enlighten me as to where the engine ID number can be found or what motor this is so I can fix her? Thanks, Lp:smokin:

390's are very wide, other than that can't help with id, sorry. The burnt piston however is indication you need to find the problem instead of just fixing it or it will do it again. The burnt up side of the piston means it has run incredibly lean. Spark knock is the first sign, ever hear any? If it was just built maybe they upped the compression alot, which would require good high octane gas, cheap gas in a high compression engine is a recipe for this. Good gas is actually more resistant to ignition, not more explosive. Cheap gas will light under compression, before the spark that is supposed to light the fuel/air mix actually does, so when the the firing system sparks it lights the mix also, then the two or more flame fronts collide, that is the "spark knock" that is heard.