A
364 is probably your best bet if you can find one...it was meant for the 82 series and later tractors, but had an adaption package for the QL tractors. This means it would also work on the 149. The adaption package is probably going to be impossible to find, so you'd have to make whatever isn't there or is wrong. Since by 'machine shop' I'm assuming you mean mill and lathe at a minimum, that should be no problem for you.
The 450 and 451 would for sure physically fit. The 551 had some slight changes to account for the different height front axle of the later 'cyclops' series tractors and may not fit quite right on something earlier. The 450 would have the appropriate diameter pulley; all you would probably have to do is get a 1/2" pulley of the same diameter of the 5/8" one it is equipped with. The 451 has a different gear ratio and would require a smaller pulley to get the same speed, which will give you less than ideal belt wrap.
All of these are extremely heavy (my 364 that I linked to above is 300#), so you'll need to make sure your steering gear and related parts are in tip-top shape...you need all the help you can get.
Of the 364, 450, and 451, the 364 is the most robust design IMO. The 450 and 451 have rather complex drive and lift systems.
Another (probably much cheaper, but more time-intensive) option would be to find some random off-brand 2-stage and adapt it.