bigedpa - I did a bit of searching in
GMpartswiki and came across a later Master Parts Book that shows those are listed as GM# 7450385 and HYATT CK 11445 X as the later replacement to your original part number info. I'm not sure if the National number is a good cross reference or not, but a little web searching shows that
Chev's of the 40's offers Part# 7450385, listed as the correct bearing for your application. Looks to be a decent price, at least compared to a few NOS GM bearings I found on evilbay. Also a better price than the National KC11455Y I could find for sale too.
I think you will find the quality of the Chev's of the 40's bearings to be comparable to the GM originals. Others will probably chime in with additional info.
