The '74 4x4 chassis (which is a GMC) had a SBC 400, but i swapped that out for a BBC 454
(which came out of a '78 GMC Suburban i scrapped)
For some reason I ALLWAYS end up getting GMC's, not chevys ,,,, My '73 prerunner Blazer... A GMC! just worked out that way.
Anyway I shortened the frame 17" AND Zee cut it up, in the front or down in the rear to better match contour of older floor/body. Result; no big gap between cab and forward to core support!
i reused some old frame channel to fill in top and bottom gaps. which completely isn't shown. the bottom of frame got filled in and I will "box" in the back.
'62 now sits on 4x4 chassis nicely