Another option that I have used successfully for transmission, crossmember, engine, etc. mounts for years is rubber grader blade material, it comes in 4” x 1” x length at many truck parts stores. Easily machined(put in freezer first for easier machining). If you can’t find any nearby, I can ship you a piece.
Ed
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'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.