I put one in my TR4a (same windshield and frame) no problem, I put one in my TR250 and cracked it in a real bonehead move getting the last bit of rubber in place.
I had a guy install the replacement for the one broke, Safelight franchise, you may have heard their ads, they found one in a regional warehouse, price installed at my home when bought from them was a little over $200 I believe, I don't think the windshields are that much less, when you add shipping, from the usual suspects.
I watched the guy put it in, I would not hesitate to do one myself after noting what I did wrong and he did right, too lazy to go into it all now, but if someone is interested I can type up some tips.
Greg