[Roadsters] Bell housing front cover question

[Dewey Hahlbohm]

Hi all, I am planning to put a 4 speed tranny behind my 2000 engine for improved gearing for autocross.  I have read you must use the correct bell housing front cover, for the tranny you are using, if you swap trannies on the 1600 or 2000 engine. Does anyone have the thickness measurements of the different front covers for the 4 speed and 5 speed trannies?

I recall reading something about different thickness front covers cause increased stresses on the throwout or transmission bearings.  Does anyone know the specifics about that, or any other reasons for being careful with the front covers?  

TIA, Dewey Hahlbohm