I'd be concerned about missing the front engine mount crossmember. Does the radiator also bolt to that, and does it help tie the frame together at the front of the front springs?

Have you considered installing any new crossmember in similar fashon/design to the originals? Skip the welding and use flanged head grade 8 frame bolts where you can instead of the rivets.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-