Blacktop zetec mainly use a plastic cover, they are fine, but you could find one of the early Ali blacktop rocker cover,
By the sounds of it, you will be ok with either type of zetec,
Most things have been covered already,
As for black top blocks being stronger, I will clear it up, later engines came with a two piece sump (girdle) which ford said was designed to stop block flex, any how that boring,
Get a zetec and pop it in, wat about mega squirt?