The gt4088 has a T4, aka T04, flange - so no problem there. The vast majority of them are have a vband exhaust fitment.
Turbo Dynamics still have my GT60. Like you, they also told me a cheap price beforehand. They took the turbo for inspection and got back to me a few days later and were like "We can bodge it up for about £500 but there no guarantee it won't fail again. Or we can upgrade the internals for . . . . (they then started talking silly money and I stopped listening).
Fitting the new turbo was a cakewalk. I did it myself in less than an hour. The re-mapping was done by Ryan G, took a few hours and was very reasonably priced. Put it this way, I gave him a 50% tip.