Longbed questions

[wcstory]

Hello all, after lurking and reading for years I finally bought a truck.

1966 GMC C30 former fire department support truck. 305 V6 with 4 speed. 12,000 miles.

I also found a donor C10 LWB with bed. I was going to remove the open back utility body from the C30 and put a Fleetside on it. That plan fell apart when I found the passenger side of the Fleetside bed had rot al along the midline.

The C30 has a 133 wheelbase and the C10&20 are 127. I was going to cut a add 6" into the bed to make the Cab to rear wheel dimension work. Has anyone done this. I searched and saw longbeds becoming shorties but no long beds becoming longer beds.

Any parts suppliers carry LWB Fleetside full side panels?

Thanks