Is the Brownie a two speed(rare) or three speed? One or two shift rails? OD should be moving left shift rail aft. First two numbers of MN are max. torque rating of ENGINE, I.e. 5531, 5831, 6231, etc. aft end of Brownie might have proper emergency brake attached, if Tru-stop, new pads are available. Easy to switchover to motor home chassis. No parts are available. Another option would be a D-80 disc brake rear axle with that bolt pattern, modern ratios.

Shortening frame is much easier if removing correct amount from frame in front of rear axle than moving axle attach parts forward.

Much discussion here in ‘big bolts’ regarding wheel selection with 5/10 on 7.25” bolt pattern, frame shortening.

Ed

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.