Short answer, yes. The SM 420 was standard GM equipment until after 1967 for light trucks. After that ['68-on] they went to the SM 465. Same bell housing -- almost. Smaller interior diameter on the pilot hole. Both bell housings fit L6s and SBCs. I don't have casting numbers at this hour, but I could look later.
I/I #4101
'71 GMC Jimmy 350, sm465, np205,3.73 posi.
'68 C/10 Stepside 292 (.030 over) Offy Intake, 500 CFM AFB,Clif headers, sm465, 3.73 posi.
'67 K/10 454 project.
'72 K/5 rolling frame project.
| 
