[FinnDiesel]

[QUOTE=dsraven;9181379]maybe something in here with a frame drawing, dunno. they have updated the site and dropped some of the early years.

Thanks, that GMUpFitter site is a great service to all of us hot-rodder types.
These are what I was examining . . .
'03 Dually 3500 (1-Ton) has a 167" wheelbase.
'55-'59 3800 Series (1-Ton) has a 135" wheelbase.
There is a nice flat spot in the frame rails approx 48" long in front of the fuel tank just looking to be sectioned.