i'm buying an adapter for a 400 to a 205 and my question is what the difference between them the seller said this adapter was for a long slim 205 not round. what years are the long slims from vs the round ones. and is there a difference in the 400's thanks

the 'long slim 205 pattern is the earlier one.......like up to 1982 or so.
the round pattern 205 is only on the later trucks....like crewcabs from the late 80's early 90's
There is a difference however in the actual 205 cases for the turbo 400 they have a bigger bearing bore than the turbo 350/465 versions
make sure that the input to the 205 you are buying has a female 32 spline
otherwise the internals are the same..............:D