Are 6 cylinder frames the same as V8 frames?

[kxnomore]

I'm considering doing a swap of the entire cab, body, engine, trans, running gear etc, from a 1972 longbed Big Block C-10 onto a 1968 shortbed, straight 6 C-10 frame. I'd be keeping the bed on the shortbed, of course.

But it appears the 1968 shortbed frame (original 250 6 cylinder) has a riveted in cross member near where the bolt in crossmember is on the 1972 V8 frame.

I am now second guessing the whole thing. Is this crossmember the only major obstacle/ difference and is this a relatively common process?

Thanks in advance.