I read on a Merkur site that you can use the Camaro/Firebird T5 tailhousing and shift fork/rail/side cover assembly to move the shifter back about an inch, pretty close to inline with the stock 4 speed and the T9. Should avoid having to cut the hole bigger. I'm going to be doing this to my car, I'll post pictures when I finally get it done. I've looked at both trannies in person and measured to confirm this. The shifter hole is almost exactly 1" further back.
88-up F-body T5s are WC, 87 and below are NWC. I believe either can be used, you just have to make sure to use the oiler and such from the same transmission. There's a lot of info out there for using S10 tailhousings on other T5s, the swap should be pretty much the same just the shifter will be moved back an inch instead of forward like 8 with the S10. The speedo gear is a bit more of a problem but doable. The hole is 2" further back so the gear needs to be relocated on the output shaft.
http://www.jalopyjournal.com/forum/showthread.php?t=280529Mustang tail housing:
Camaro tail housing:
You can visibly see the difference. I think the mount location is the same but I don't know for sure.