lifter bores are slightly taller on a roller 360 block. three mounts in the lifter valley for the lifter hold down spider.

Other than that it's pretty much the same as any 74 and up 360 (main bearing changed in 74).

Best heads are the magnums, which oil thru the pushrods so the block oiling provisions are moot there. The heads your 91 came with are probably the best stock LA heads out there, but the magnums are enough better to warrant the change.

http://www.hotrod.com/articles/mopp-0308-adding-magnum-to-a-360-short-block/
http://www.hughesengines.com/TechArticles/11convertingmagnumstyleheadstoworkonthelablock.php

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