Chiphead,
Looking at the '59 parts book, I found the following entry.
1.649 WASHER, Oil Pump Thrust
37-55 ALL, CORVETTE (6 cyl.).......(1/2 I.D. x 7/8 O.D.) ..... p/n 838472
Diagram shows it between pump and distributor gear.
The oil pump listing are:
40-52 ALL,
53 ALL (exc. P.G.) ... (body cast 839159)..... p/n 839157
53 PASS., CORVETTE w/P.G.,
54 ALL, CORVETTE,
55 CORVETTE, COMM., UTIL. (1st Ser.) ... p/n 3702363
55-59 PASS. (6 cyl.),
55-59 COMM., UTIL. (6 cyl.)(2nd Ser.) ... p/n 3836203
If they redesigned the end of the oil pump housing to eliminate the thrust washer you may have found your problem.
The TRW engine parts book shows for Chevy Trucks 235 c.i. Part No 50012 (Chevy # 3702363) (unique to '54), for the later 235's it shows Part No 50019 (Chevy # 3786293) thru '62. For the older 235's it shows Part No 50001 (Chevy # 839157).
The TRW book also lists oil pump screen assemblies. What year pickup do you need? I can give you the TRW number which might help you find a NOS one.