69 shortbed on 85 longbed frame?

[hawkeye1101]

Hello everyone,
What a great message board, I've been lurking here for a few days and I have already found lots of useful info here.

I am still trying to decide what would be involved to put a 69 GMC shortbox body& bed on a 85 Chevy Longbed 1/2 ton 4x4 frame.
The 85 has the engine/trans/transfer case combo I want already.
So I have a couple questions.

1. Obviously the frame will ned to be shortened in the middle(and shorten the driveline etc.) and the very back cut off. Does anyone have the length of those cuts already figured out?

2. How many (if any) of the front body/cab mounts on the 85 frame will match the 69 body? Will the radiator support, and front cab mounts be able to stay where they are?
I think the late model cabs are longer so I imagine the rear cab mounts would have to be moved forward.

If this has all been discussed before please direct me to it....I've not had much luck finding the info I need with searches disabled.

Thanks in advance for any info.