I agree with DPC on my 500 from Kiesler: I did the auto to 500 swap in my 440 ebody, and you do have to cut the floor, which personally, didn't matter to me.
All of the parts were of top quality down to the transmission mounts.
I also did a muncie M-22, 4 speed to the tremec 500 as well in my 67, BB, Corvette Roadster . That retrofit did not take any mods at all
But the tech and sales personnel were the worst that I have probably ever encountered in the hobby, in both cases
Myself, again, I don't speed shift anymore, but I do high-rpm shift at times. But in speed shifting I dont believe the inherent long throw in the pistol grip that comes with the kit is really something that is realistic anyways. Thats just me
But in the M-22 to 500 swap I did in my Vette, the short, stock type shifter did allow for speed shifting, and I did not have issues
It is odd that some have high rpm or high rpm shift issues, although 1000's have been sold, and many say they have no like probs