Trans Specialties built the trans for my car. You'll want to ask what speedo driven gear the trans has on the tailshaft. You'll want to have a 15 tooth drive gear. Easy enough to change. Their basic trans come with the 34 element sprag/drum. Mine held up well with the stock input shaft and forward hub for 6 years of street use and couple hundred passes behind the 469" motor. 1000 miles and 30 passes behind the 540" and the stock input shaft ate the splines from the forward hub. That got replaced with the 300M input shaft and billet hub. Questions are where do you stop, how much risk do you want to take? I was told the stock input shaft/hub is reliable to about 800HP. 300M input takes it to about 1000HP, also adds roughly $300.00 to the tab. You can quickly get to $2,000.00 in a trans built to take a beating.
PS - converter I was running behind the 540" was their 10" XHD LS (2900-3300). When the input shaft let loose, we had swapped in a one of a kind Coan 13" 2400 stall that I had Coan build. That converter was great for low speed street driving, but proved to be a little harsh at WOT shifts behind the 540". So, went back to the T-S XHD.