I think part of the modern FI allure that entices the carbed crowd comes from the element of computerized control as much as the actual injection. Modern fuel systems incorporate not only fuel curves(and usually indv cylinder injection) that automaticaly adapt to load and ambient environmental variations, but also alter timing to increase power and decrease detonation in all scenarios. heck, I can even program a seperate fuel/timing table that would go into effect should I get a tank of crappy gasoline. That tends to be a little more difficult with a distributor. The benefits of a good TR6 system would include better gas milage, more power, easier cranking, and better overall driving manners. Having said that, I don't think a really good FI system has been produced for this application. I think two things really hold back the benefits of any induction system on this engine: manifold design and lack of ignition control. Honestly, I don't think the side draft design is such a hot idea. Even if you could get the air flowing well enough through the runners, I don't think the imperfect atomization of the mixture allows it to behave in a beneficial manner over such a horizontal distance.
Now, if you could pop an injector into the runner of each cylinder and angle it towards the head, I think you would be in business even without ignition control. You could still use TBs and maybe a speed density unit to meter the air on the end of the manifold, you get the charge moving the length of the runner without the impedence of (comparatively)poorly atomized fuel, then hit it with nice, FI, computer controled, atomized fuel as its entering the head. There may be some trouble with the the angle of injection and the angle of the port entering the head. I would hope it could be minimized.
That may not be the most practical approach, but I think it would help with one of the major drawbacks of the TR6 induction system. Next up: putting the frigging exhaust ports on the other side of teh head.