Brownie trans. Come in sizes, first number indicates TORQUE rating of ENGINE I. e. 500 ft. lbs. of 5531, etc. OK for early 5.9. Anything larger than 6000 series is too large for most vehicles, unless one has an oilfield truck. The third number indicates the number of speeds, I. e. 3 in this case or 4 in 6241, no gears are synchronized, practice your double clutching, works easily. All are designed for divorced mounting. Some do not have a rear seal, just reverse threads which do not appear to be a problem.
They are shifted by two rods going fwd to factory shift tower which has many bolt holes for mounting brackets. Best to get one of these, although one could be made(see top of frame in picture.) Shift linkage can be .5” water pipe or 1“ EMT. Speedo output on rear of case.
Trans. mounts to two factory crossmembers that are rubber mounted to truck frame. Input side has a rotary mount that allows the rear crossmember to take the torque load. Mount could be replaced with short section of 6” or 8” heavy pipe attached to crossmember. Rubber grader blade mat’l (1” thick) handles vibrations. Rear crossmember handles torque and park brake(TrueStop, new pads available near Denver, CO) mounting. Very complicated to replicate. It is best to have a park brake, unless one has spring brakes. Probably illegal, too.
One can be mounted from beneath, but it is a lot of work. A good excuse for mounting would be to occupy the location of aux. accessory like water pump, etc. in middle of driveline. Of course one needs two splined driveshafts, etc. Normal shifting
Ed