I don't think anyone has attempted a 300 to 350 series swap that I have seen.
A side from a 300 having a straight/flat frame out back behind the cab, I don't see why it couldn't be done as easy as the 100 or 200 series.
I do know the 300 frames are taller and thicker than a 100/200 frame for sure, so I would guess that you would be limited to using a 350 front clip or the frame rails won't line up properly to do a proper "Z" cut and splice.
I would just do some preliminary measuring to see what the frame dimensions are and go from there. My guess would be they are the same, because the 61-71 100/200 are the same as the 72-93 150/250's.

Now that I'm thinking of it, the other thing I would look into is the fact that the 300 and up frame rails are flat/straight behind the cab. You might not have to even cut/clip a 300 and up frame. Just do a whole frame swap and weld the 61-71 cab mounts onto the 72-93 frame and modify the front cross member as needed on the 150/250 for radiator clearance.....even that might not be needed where the cabs are mounted high on the frames, just a thought.
The only reason for clipping the 72-93 IFS on a 61-71 100-200 is the fact that there is a higher offset in the frame rails over the rear axle, but you won't have this issue on a 300 and up.

Now, I'm not sure if the dually pickups 72-93 had an offset over the rear axle? I know the cab and chassis didn't. So, you might run into an issue there......

Mark D.

1968 W200 Sweptline
1969 D100 Utiline
1971 D100 SE Sweptline
1993 D250 Club Cab Sweptline
1986 W250 Cab & Chassis
1978 D300 Sweptline

E. Brookfield, Massachusetts



Edited 1 time(s). Last edit at 10/23/2017 12:38PM by swptln.