The Fram Filters cross reference guide for NAPA 1521 lists Fram PH43.
PH5
yes
Both WIX and Fram provide on-line cross reference systems The sears # will probably be a suppliers # rather than a unique Sears # and the Cross reference system should work fine.
It does cross (with some searching) would be a wix 57099
That would be a Fram CA8235
That would be a WIX 42362
The equivalent NGK plug would be B2LM
Gates Belt #6690BR
Napa 3986 racor r120t
The places to purchase Ingersoll watches are many and varied. The best place to start would be Amazon. If you are on a tight budget, a good option would be to try eBay.
That would be a CH9018.