Neat project. I am a rotary enthusiest second, and a British car lover first. My first car was an unrestored '74 TR6 which I daily drove through most of high school. I finally saved up enough to restore it my senior year. That car was ridiculously reliable, easily the most trustworthy car I have ever owned. I rebuilt the factory stromberg carbs when I bought it and never had any issues. Those cars are super simple, there just isn't much to break, and if something does break it only takes 2 seconds to find it and fix it. Now it has a high compression, cammed engine with more tunable SU carbs. It is a blast to drive.
I too have contemplated restoring an older british roadster and swapping a 13B-T in. Although I would choose a smaller chassis like a spitfire, midget, sprite, etc. I love british straight-6 engines too much to toss one out. Right now I am on the hunt for a good condition TVR 2500M.
Good luck.
Oh yeah... one more thing:
I would make sure to reinforce the diff mount. They tend to crack with any kind of performance driving.