I had to do same job on two rear frames a few weeks ago, Argentinian history as you can guess. My approach was to disengage the upper tubes from the doweled lower bigger tubes . You cannot possibly rectify the lot with all joints bolted up - and no good way to use brute force under a press. This would lead to curved funny shapes as you´d get bends where there were no before. Mostly snake like shapes then. So I got me the big welding torch after undoing the scews and levering the upper tubes out of dowel fits. So you put some big tube or monkey wrench on the rear end and heat at the suitable place to red and bend to your liking. You´d want to get axle of taper roller bearings parallel, resp. horizontal when viewed from behind, plus the wheel axle parallel as well. I made me two lengths of plastic disks to fit in the Timken bearing seats with central bore for pushing some straight stainless rod through to be placed on v-blocks or parallels on a table. So then you check the wheel axle slots for same heights left and right. Otherwise you´d have a rear wheel not vertical !! The shock absorber bores are not critical here, they may be allright after having all else in positions.
Once you got the lower big tubes correct with swing arm bearing bores horizontal and parallel on your table - plus rear forked ends parallel/same height too, you then look at the curved tubes on front and the upper tubes that have to engage the dowels again. For arriving there you have to think about where to go with the torch, either bending the curved tubes back when too short to reach the dowel. Or maybe just bending down or up when the loose ends are too high or low. Depends on what defect you got.
Anyway, with the torch you can feel the redhot tube to go where you want it, some lever force is certainly required but you get good control about what place has to give for the job to be done. A few hours will go for sure, but this depends on your standards of perfection then.
In case the forgings at the rear are f***d up a lot you could consider to have some welding done for perfect seating of nuts and spacers of the wheel axle components. Big washers are desirable, not original but an improvement, so you don´t squash faces again later.
Vic
Once you got the lower big tubes correct with swing arm bearing bores horizontal and parallel on your table - plus rear forked ends parallel/same height too, you then look at the curved tubes on front and the upper tubes that have to engage the dowels again. For arriving there you have to think about where to go with the torch, either bending the curved tubes back when too short to reach the dowel. Or maybe just bending down or up when the loose ends are too high or low. Depends on what defect you got.
Anyway, with the torch you can feel the redhot tube to go where you want it, some lever force is certainly required but you get good control about what place has to give for the job to be done. A few hours will go for sure, but this depends on your standards of perfection then.
In case the forgings at the rear are f***d up a lot you could consider to have some welding done for perfect seating of nuts and spacers of the wheel axle components. Big washers are desirable, not original but an improvement, so you don´t squash faces again later.
Vic