just simply replacing everything, new idlers etc is usually a quick job. But when you start just putting new bushings in the front idlers and changing the old pads from the old rails over to the new rails is when time becomes intense. With new rails and pads already together and just changing out the idlers and rollers myself and my righthand man can do a D8 undercarriage (if we don't have to plug weld and re-tap roller bolt holes etc) usually in a big day and a half.
We take the track frames right off and flip them over as well, farting around with a home made roller holder on a floor jack is too time consuming, plus its nice to really put the torque on them when installing the new ones. We have a zoom-boom and an 8 ton picker truck at our disposal as well, find it alot faster doing it outside infront of the shop.
I don't know if you have ever read in the old Caterpillar manuals how they suggest you jack up the cats, I find that much too time consuming as well, I just stack up 2 feet of cut up old railway ties and drive the front up on them, slide by big homemade saw horse underneath and back it back down untill it sits on the frame just behind the rad pan bolts. then do the same thing at the back except jam the railway ties in as close as possible to the grousers and start backing up, the cat with climb vertically before it can go backwards. then i slide my homemade jackstands made from 105 lb per foot 12 inch I-beam underneath the rear just beside the wishbone bolts. and then drive it ahead again untill it sits down, keep driving ahead untill the blocks spit out the back haha.
you learn all kinds of time saving tricks.... usually after you do it the long and hard ways first lol.
