I'm a bit confused by this (newby :-)
But I tripped over a Very detailed Caterham SV 'clone', with Miata bits, build in Locost USA site.
http://www.locostusa.com/forums/view...p?f=35&t=13510
Apparently the Caterham SV propshaft tunnel is 4" wide.. outside to outside dimension, then it narrows to the rear by 1/2"
Seemingly his Miata bits fit.. just.. but well, nonetheless.
The chassis is 43 1/2" wide, in total, at the widest point.
No mention of propshaft diff offset issues.
Could certainly have been some.. but none were even mentioned... odd.