Over the past week and a half, I have reattached the frame crossmember and brackets that were removed from the old frame, assembled both the front and rear suspension, all four brakes, installed most of the brake lines, and set the engine back on the chassis. I also dug the cab out and set it on the frame so that I can begin working on that.
As suggested by 62Stick, I reattached the transmision support crossmember and parking brake equalizer crossmember with grade 5 bolts. However, I used grade 8 on the cab mounts, trac bar bracket, radiator mounting clips, and upper shock mounts since they do not need to flex as much as the frame crossmembers.
I had a few minor setbacks with the suspension and brakes that prevented me from getting it together sooner, but I am still very pleased with the progress I have made. First, I had forgotten to order the u-bolts for the lower a-arm shafts, and calls to all of the auto parts stores in the area revealed that they were not available locally. I ordered them from classic parts, and they arrived within a few days. I also realized as I was puttinbg the last brake drum over the last completed brake assembly that I had forgotten to install those winged washers that go on the anchor pins and help keep the shoes in place

. So, off came all of the wheels and brake drums, and shoe springs again.
I used OE style rubber bushings on the trac bar, but I went with urethane rear control arm bushings, because they are easier to install.
While I was working with the front suspension, my grandpa and a friend of mine worked on reinstalling the pre-bent stainless steel brake lines. We were able to reuse all of the original junction blocks. I bought the ten piece brake line clip set from classic parts, but I can't remember were all of the clips go, so I'll have to do some research on that.
With some help, a tractor and an engine hoist I got the cab set on the frame so that I can start rust repair. Every time I look at that cab, the rust problems seem to get worse. The main one is the floorboard, especially on the driver's side, right were the rocker, kick panel, and floor board all come together. I have no experience welding pach panel, and it seems that cutting out that critical area to weld in new panels would make it very easy for the cab to get out of alignment, so repairing that rust is a rather daunting task. In fact, that area has deteriorated to such an extent that moving the cab 3 times make have already messed it up. I am toying with the idea of getting another cab in better shape, if my budget allows.
I am having a lot of fun tracking down information on my truck when I am not working on it - I downloaded the info package or my truck from the GM heritage center, and have spent many hours looking it over. Among the information is a list of available options for my model truck (C1504). One of the options listed is "G50 - Springs, Rear, 2000 lbs each." The more I look at my springs the more I think I have this option. I have a full set of half ton springs from my spare frame, and the rears on my truck seem much beefier. I have never heard of anyone else having these heavy duty springs, which makes me wonder how rare they are. My shop manual gives measurements for both types of springs, so I should probably measure them sometime to confirm that. My GVW plate reads 5000 lbs, but its a little hard to tell from the wording in the manual whether that is the GVW for that particular truck, or if that is just the maximum possible GVW that truck could have if it was optioned right.