I'm putting an 85 Celica in my TR3 in a week or so.
The 'kit' is made by a local guy in our club, I drove his Saturday and it was really nice. He's put them in about 15 cars so far, all local.
You use the TR3 bell housing with a welded on ally adapter plate (must sacrifice your bell housing as its cut from the tranny at 8 1/4 inches then welded up in a shop) for the Toy tranny, use the stock clutch actuator, the stock flywheel, stock plate with a Toyota clutch disc. He makes a tranny mount that can be rebushed. Stock drive shaft with a coupler made from the old Toyota driveshaft tranny end. MG converted angle drive for the speedo.
The parts look really well done and many in the club have put a lot of miles on.
Much much cheaper route and that's my reason for this route as I'd rather keep my stock tranny but not enough to go without that extra gear, it'd probably just set in the garage anyway.
The only mod is that the gearshift will set back 2 inches from normal (no mod piece for that) so the tunnel will be cut back some).
I'll take pics when we do the work.
This will save over a grand of buying the kit.