modify bellhousing??

I talked once on the phone with Brewer's about putting an OD trans in my car (early A). They said you have to switch to the 4.8" retainer on the trans & then machine the opening on the bell housing larger to accept the larger retainer. I know this isn't the exact same situation as yours but the info about machining the hole in the bell would still apply. If you've got access (free?) to the machines & machinist, I'd go for it.