jcarter, you mention grinding "a bit of the flange on bottom edge of the frame to make sure there was enough clearance."

I just repaired the frame on a 66 Chevy truck that had the frame notched to fit headers, only removing about 1/3 of the flange in a few places.
The left frame rail frame was cracked just behind the front suspension cross member and lacked about 1" of being broken in two pieces. The truck was driven to the inspection station where it was rejected....
I would be very careful when removing the flange of a frame. Be sure what you remove leaves a big smooth radius to reduce stress points.
Keep an eye on it for cracks.

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-