I have a small block from my neighbors car casting # 3870010 frt pad 151476261 KO 5 28 No casting date in bell housing area r/s of block 5 E 21 with the clock next to it. No vin by oil filter. What the heck is it ??

More than likely the casting number is 3970010 which is a fairly common 350 block.

151476261 is the VIN derivative of the car this engine came from
1 = Chevrolet
5 = 1975 model year
1 = Oshawa Canada Assy Plant
476261 = last 6 digits of the cars VIN

Oshawa built Monte Carlos and Chevelles in 1975

K0528 (look to see if there is a 3 letter code after this number)
K = McKinnon Engine plant
0528 = May 28th

5 E 21 = is the casting date of May 21, 1975

Looks like a 350 out of a 1975 Chevelle or Monte Carlo

Thanks Jonesy.. In all my years of messing with this stuff I've never seen one without a casting date in the bellhousing area.