I have a std. bore 396 4 bolt main block with a casting date of oct. 30 of 1965. It has a suffix code of EF which says it is from a 1966 chevelle. The casting is a 962. So my question is, did they utilize 4 bolt main blocks for the 360 HP motors or was it a 425 HP block miss stamped? thanks for any comments !!!!!!

I would say it is a block from a 66 chevelle with 375 horse not 425, this was a fairly common engine in 66 while in 67 they only made 612 of these monsters. Only difference in 375 and 425 was intake and exhaust versus 66 L72 Vette engine (425). You got a good one there take care of it !

Some of the early 1966 model L34 blocks were 4-bolt main. During the run the L34 became a 2-bolt main block. Yours has a casting date of October '65, so it is probable that you've got one of those early 4-bolt L34s.

The L78s were always 4-bolt main equipped. They also came with domed, forged 11:1 pistons and square port heads, plus a solid high-lift cam.