I read an old motorcyclist magazine (I think) write up on the gt250 back in the day, and I think they hit the nail on the head. They pretty much said that Suzuki made a 2 stroke engine that acted like a 4 stroke. That may be a slight stretch, but In stock dress, there is nothing that really that stands out power wise, it just seems pretty even keel/no frills. Smooth acceleration, power band doesn't hit super sharp, no real "on the pipe" feel to speak of. Just a fun little all around bike. they never did compete well performance wise with the rd250/350's of the day, and im not convinced they were really meant to.
Anyhow, I think it would be an ok powerplant, as long as its a 75 or earlier (ram air head engine) 76 and 77 changed a bunch of little things throughout the engine, and that can make getting some parts a real pita. (3 bearing crank with oddball bearing and seal dimensions, changed cylinders, carb mounts and ports)
If I get another one, im planning on a 75 or earlier just to not have to deal with the scarcity of some of the parts. If it weren't for one place in the uk, I wouldn't have crank seals (or a running motor)
The other benefit, however small, is that its a 3 bolt cradle mount setup, vs the 350 setup with the top engine mount. could simplify things a bit