pulley part #s
 

wp 3995631ao 11
crank 3751232bb

Anyone got any idea what these are for? They're for a small block I believe, if that helps...

Re: pulley part #s
 

I believe WaterPump pulley #3995631 AO is for 1971-75 Small Blocks w/61 Amp Alt,..not possible on a Solid lifter SB,and 1973-74 ALL w/454 CID.

Crank Pulley #3751232 BB is for nearly Every Small Block 1965-68 Corvettes(w/AC)-Trucks-Passenger w/Hydra lifter 283 & 327 & 350 CID w/P/S,and 1964-68 Chevelle-Chevy II-Camaro w/Hydra lifter 283 & 327 & 350 CID w/P/S but w/o AC...and 1975-77 Monza 262 w/o AC.

Re: pulley part #s
 

My 70 Chevelle assembly manual shows #3995631 AO as being correct for the L34 and LS5 Chevelle also.

Re: pulley part #s
 

You're right Rick,there is a revision noted for those vehicles built w/AC after 6/3/70,which coincides around the time this pulley was first produced.
It looks like this pulley was as a replacement part on late 1969 Big Block & Small Block Hydra lifter vehicles WITH A/C as well as original equipment from LATE production 1970 through 1976 vehicles with same.