I'm personally very interested in the proposed combo of Borgenson fast-ratio box (because its claimed to be ~15-20 pounds lighter than a Mopar ps box).. mated with the longer Mopar "Fast Ratio" pitman arm.... any possible mechanical interference issues (with headers.. small block)
On the Mopar ps gear boxes, all that is really done to make it "fast ratio" is the longer "fast ratio" pitman arm.... which can be attached to any Mopar ps box... simply the shaft size is the determining factor (small 1972 and earlier, large 1973 and later; all "T/A" boxes have the larger size shaft). The internal worm gears are the same between a T/A box and non-T/A box, but the T/A box has internal stoppers to limit the radius turn with the longer pitman arm. In fact, if you want a tighter turning radius, then use a non-T/A ps box with the longer pitman arm... BUT.. you'll have more inside tire rubbing interference with the frame rails at the rear of the turned tires.
I've just had my T/A box rebuilt by FF.. Stage-3... but... I'm still interested in the LIGHTER WEIGHT BENEFIT of the Borgenson ps box.. and the potential to quicken the steering even faster than the T/A fast ratio box.
WITH the longer fast-ratio pitman arm, be certain to also install the longer C-Body idler arm... that is what is commonly being referred to as "fast ratio idler arm"... again, simply a C-body idler arm (Chrysler was aware of the matter of not including that longer idler arm with the fast-ratio ps box/fast ratio pitman arm... but, they ended production (even into early 1971 models) without ever including the longer idler arm... result is one side turns tighter radius than the other side.
IMO... fast steering ratios are great and fun... the quicker the better.. for all reactions ... AX pylons and high-speed track runs.... I've quickened my steering even faster by using a smaller diameter steering wheel... 11.5" diameter... helps get through the pylons very quickly.. as well as on hi-speed road course manuevers... highway driving is also safe and more fun!
IF you do install the Borgenson ps box WITH the longer fast ratio pitman arm (and don't forget the longer required idler arm for proper turning radius lh/rh), please keep us informed .... T/Anks ahead and good luck!