Your gonna want to jig it up so everything is square and in its proper place and at the correct elevation in relation to each other. Dont want it to be crabbed or listing. Yes 4 hours give or take. not counting removal of the cab of course.
The jig need not be an elaborate thing. If it were me I would mkae up an X frame out of .25x2 strapfrom the 4 cab support locations on the frame with a 1 1/2" angle iron frame around that to keep it square, and factor in the differnt elevations front to rear using tubular steel (pipe) or a stack of washers to shim. Bolt the cab mounts to the jig set the cab either onthe jig and mounts or flip the whole thing over and lay the jig and mounts on from the top. No overhead welding thata way. Overhead allways sets my beard afire.
I was raised up north. Farther north than I care to admit. Anyway these old trucks the gen 6s and 7s were brand new then. The way these cab mounts are built they tend to hold the road salt and mud there for rust out over time. I had a 70 model when I was in high school that was so rusted the wieght of the cab rested on the steering column that made it a real treat to drive. I tell you this so that you understand that it will only get worse. One day you will pull out in traffic making a right or left turn and the steering wheel will fail to unwind on its own. and depending on your reaction time, speed, and the attention of other people sharing the road that day, well you see where I'm going. If ya got the parts and the time. best fix it now. why wait for the enivitable. I already told you how I know. And as for the jig, thinking about this last night I decided I may have led you astray abit. If you are using real replacement cab mounts that are good reproductions of the originals, with flanges and what not. the jig may be overkill. I say this because if'n the mounts are the only issue and the floor/attachment points are solid then I see no reason not to wash the old ones off at the spot welds (after taking several reference measurements and a quick pencil sketch), and plug weld the new ones on. Yea the more I think about it the more I agree with my new tact. put em on and let the bushings do there job at taking up for SMALL errors in attachment.
Can't say but the ones in the Carpenter catolog look as close to original as any I have ever seen. We used to jackem up a little and get them close to right the scab in some plate and angle right over the old ones. But me and my brothers had no money or sense. nearly burned one old truck to the ground doin that.
So, from Mac's pictures it appears they are similar to the one's at Dennis-Carpenter?
Haven't had a chance to begin on the lead-filling yet. Bought a piece of angle-iron the other day to melt my lead ingots into for lead sticks. Hopefully I will be able to get to that this weekend.