I looked at the 2 Chrysler 540's I have, both input shafts stick out from the front of the trans about 7.5", 1.5" spline, 17 teeth on the cluster drive gear(about 3.25" O D), Px if you wish. Easy to get clutch disc w/ variety of spline counts from clutch rebuilder; 1" +/_ thick adapter should be easy to make, take care of Chrysler shift rail stick out. Chrysler is only one w/ this stickout, so, if it is a problem, a top shifter cover from other make will fit, however, there are at least 2 styles of shift covers that are hard to tell apart, so make sure to get a guarantee that another one will fit before you purchase it. Make sure pins at top of shiftcover are tight.

'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.