This may not be true for all model years, but vintage engine blocks have casting dates as well as part numbers on them. My "new for 68 5L engine" block has both sets of numbers, visible when the starter is off.

 

Well, if the 86 did have a different block, then the part # was for that year only. I've disassembled and rebuilt several 302 roller engines and I've only seen E7TE's and E5TE's. There may be something in the other numbers cast in the same area but I have not found any rhyme or
reason to them. There is also XXX cast into the lifter valley on some, YYY on others. I've never met anyone who knows what they mean.
Oh yeah, there is nothing heavy duty or better about any of these stock roller blocks, they all split the same.

If you want to know what pistons they have, the part # is on the top of the piston #E7ZE are the good ones.

 

Sorry I was out digging up old threads again, And I found this very interesting on how to tell witch year the block is.