Okay; I'm back from vacation.
Russ; I don't have complete bills for every T5 anymore; however, a -908 is a very early casting. I found a -907 and a -909, and -904 which are all NON World Class.
I do not have one to be able to check your measurement. I would call GF/Astro and give them your casting number; it's almost certainly a NWC case, and I do not know if this is suitable for their gears.
With respect to the bellhousing; if you and the producer of the gearset feel its alright to use the case, then drilling and tapping to suit is not a problem.