You MIGHT be able to get one through Ford or International.
1997 F-250HD Extended Cab 4x4 7.3 Powerstroke
3" Down Pipe to 4" Exhaust (Stainless) ~ Tymar Intake w/ AFE Big Boost Filter ~ TS 6 Position Chip ~ HPOP Cross Over Line ~ Regulated Return ~ E-Fuel System ~ Intercooled ~ CCV Mod ~ Dual Aeroforce Interceptor Gauges ~ Dana 60 Swap
If i were to do it i would either find a good, used factory motor with low miles and run it. For the most part they will be more reliable than any motor you have built. I've seen a ton of factory built 7.3's run forever, while there are a **** load of 7.3's that get re-built and don't even make it to 100k before they are dead again.
But if you want a crate motor built, whether its stock or wild, i'd go with either Unlimited Diesel, Swamps Diesel, Beans Diesel, DI Performance, or Wide Open Performance. They won't be as cheap as the shady places like the place that makes the Black Mamba, but the quality will be better and they will actually stand behind their work and not screw you over.
97 F-250 ECLB 7.3/E4OD/4wd, 216k miles: FFD 250/200%'s, stock turbo, built trans, e-fuel, Swamps IDM, shimmed 910's, Melling LPOP, welded cam gear/modified pick-up tube. Built and tuned by me