buoymaker, I haven't the experience with the rear axle bearings yet to answer the questions about fitment and installation, but did check to see what is being offered for replacements for the GM# 111121 bearings. You might check this offering
FS-315 that the Filling Station lists as a direct replacement for the original GM# 111121 and alternate Hyatt OR1502.
On another note, I did find this
listing that seems to indicate the R-1502-El is a compatible interchange. This same number is also listed for cross referenced as a replacement for the Hyatt C1502 (current designation for the original Hyatt OR1502 number). Anyhow, hope this might help answer part of your questions about fitment.
