I’m using the 617 engine in a power train swap and am curious if enlarging the size of air intake on the turbo will have a positive impact on performance, as it does with other turbo diesels. Also, what other mods can be done that will increase performance without reducing durability, i.e. intercooler, etc ?

The stock setup is very well designed and won't gain much from modification or replacment.

Check out this forum for better performance answers: http://schumanautomotive.com/forums/forumdisplay.php?f=19