It will probably be much easier to locate a reasonably priced 66 carbine in .44-40 and have it converted to .44 Colt. The rear portion of the chamber needs to be cut off and the chamber re-cut for the straight wall .44 cartridge, plus possibly some minor adjustments to carrier and extractor. Through this process the barrel will be shortened by some .5" only. Had this job done to 73's and a Henry.
I'd love to see that PU ivory Porforio Diaz carbine, Gripmaker.
Bootsie