Recently bought a 20A 2822 977 that was my grandpas. He bought it new in 1958 and ran it untill retirement in 79 and then sold at auction around 1980. Its undercarriage is shot but i found another one s/n 20A3128 with a nearly new undercarriage, however the older one has the standard D69u track frame and the latter has the optional 8H2462 heavy duty track roller frame arrangement. Is there any reason I could not switch them around completely? First pick 2822 second 3128.

Something doesn't seem right. The 20A changed from D6 undercarriage (6.75" pitch) to D7 undercarriage (8.0" pitch) at s/n 20A2508. Both those units should have the later undercarriage.