I have a Mercury 8CM going together at a local machine shop. I gave them a rear main seal retainer I had sitting on the shelf and I received a call saying it was too small. I believe it's from an earlier block (59AB) but it's all I had. Is there a difference between AB style blocks and the last generation when it comes to that metal piece that holds in the rear main? My shop is not too versed in flatheads and I'd hate to spend $50 at Van Pelt's if those pieces are all the same.