Couple of thoughts here-
Depending on your mods, we can have something custom made instead of an off the shelf piece.
I can have a 76mm made four different ways;
A Y2K 76MM would have a T6 mounting flange, and a 3.955 exducer, and 5 inch DP flange. It would take some serious fuel and RPM to get on top of it. Turbine A/R is .96.
The next option would be a "mid frame" that Tom is referring to. That turbo was designed for tractor pullers 3X3 class specs. It has a standard T4 mount, 2.96 exducer, and only available with a 4 inch DP flange. It has a 3 inch discharge, and three available turbine A/R; 1.00, 1.14, 1.27. I can have a custom cover made to run a 78, or 80 mm bushed to a 76.
A step down from the mid frame is the Super T. The Super T has a 3 inch discharge, 4 inch air inlet, standard T4 mount, 2.693 exducer, and turbine A/R as follows: .68, .81, .96. DP is 3.5 or 4 inch. This unit is much easier to spool than a mid frame, but will move less air, etc
The final way is with a standard T4 series 76mm unit with a 2.5 discharge, 4 inch intake, and turbine 2.542 exducer, and A/R as follows: .68, .81, .96. DP is 3.5 or 4 inch.
Every turbo we order is custom built around your mods. We have a good idea of what works.