Never actually seen one, but have seen articles. Looks like a fairly straight forward deal, if you have decent mechanical skills.
As I recall, you use the 3-speed mainshaft, in the 4-speed case. The only real machine work, is drilling the 4-speed case, for the reverse lockout pin. And shortening the driveshaft, of course.
I'd think it would be just the thing, for a roadster, or bucket. With the 30% overdrive, and a wide ratio(3.50 1st), you could put in a 4.11 rear gear, and still
bop right down the interstate. Plus have an awesome off line capability.
In the ramp truck, with 245-75R16 tires, it cut from 3250@65, to 2400@65.
I'll tell you in a few months, if it will hold up to a 402/TH400, in a 1-ton ramp truck.