You could also just get a 73-74 trans crossmember that looks just like the one 75 stepside made.
This is my stock one 3rd from the left:
Found one of it installed:
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Chris Lucas
1973 Chevy C-10
1978 GMC Jimmy (2WD) - SOLD
1987 R10 twin turbo LS
1991 R3500 SRW CrewCab
1985 K5 diesel swapped project
1989 K5 2WD conversion w/ Vette susp Project
Captkaos Customs
73-87chevytrucks.com