I am showing what I did to put a SBC in a 1952, 3100 Chevrolet Truck.
Small Block Chevy V8 swap
I cut to fit and bolted the cross members to the engine and tranny and positioned everything where I wanted it, tack welded the ends on and marked the location on the frame with a marker. Then pulled every thing out and welded the ends on. Then I put the engine cross member in position and drilled and bolted it to the frame. Then I put the engine and tranny back in and drilled the holes for the tranny cross member.
Same for these years 1947, 1948, 1949, 1950, 1951, 1952, 1953, 1954