[blownb310]

I've just spent about 1.5 hrs searching for the answer to this question, so please bear with me if this has been asked before. I would like to identify a service replacement shortblock that I have. I was told it is a 400, but it has the valve relief scallops down lower in the deck [top of bores] like the '66 and earlier engines did. The numbers on the block are SR83414, then there is one other number on the front of the block but the first digit is hard to make out. It's either 36138 or 86138. The casting date on the rear next to the dist is L076. It's of course, 2 bolt main. What do I have here please?