yes the Chev cross member is the same for 6 and v8, except if it had a v8 then there were 2 brackets riveted to the back of the cross member to mount the v8 [cuz shorter than the 235] - the kits available from the vendors that's called 'original style' v8 mounts includes the frame brackets that you bolt on [rivet holes should be present], along with the pegs and small brackets that bolt to the front of a small block - you'll also need a fan shroud or it'll overheat at low speed cuz the fan's too far back
and yes, I think the cross members are too different to work installing a 283 the same way in a GMC - you could use whatever the GMC v8 was for 58 tho!!
Bill
