Hey Chris,
I have had a WC T5 in my 65 Fastback for about 12 years now. When I was 1st restoring it was about the time California Pony Cars came out with the conversion and, since the toploader was toast, I went with it. The only regret I have now is I traded the 4-speed for the T5 and all the gear for conversion. thought I'd had a win at the time....still, live & learn.
As for the car, still drives fantastic! Recently drove a mate's A-code 66 with a toploader (he drove mine) and we both came away preferring to drive the T5.
Best you hang onto your original parts though....