72 truck frame under a 78?

Will a 1972 d100 frame fit under a 1978 d150se with no issues??

And the final answer is: Probably!
72 being the 1st year of a new design some things are 72 specific, weather or not those specific things will effect a frame swap are in question. I suspect the basic frame will swap, providing both trucks are the same cab/box configuration.
There may be issues with things like fuel tanks, as far as I know, 72 were all in cab fuel tanks, so mounting a frame mount tank might be a challenge. Wiring will be different. Brakes may or may not be an issue. Body and cab mounts might be slightly different (especially the rad support mounts). Most other stuff should swap out as units, but may differ part to part. Hope this answers your questions.
Gene

radiator support mounts possibly I swapped beds on one once & the front bed mounts were a different height or something IIRC

I think the bed mounts are different between 2 and 4WD trucks .

Well the 72 is a 2wd and the 78 is a 2wd. The 72 frame is bare and we were going to have someone do some suspension and steering upgrades to it. Then it will go to the body shop and the frame and body will be reunited with brand new steering and suspension and a 5.7 hemi crate motor. Not to worried about wiring because from experience the dodge wiring sucks so we always retrofit a wiring kit.

Having a 72 and trying to use parts from a 77, I can tell you that some stuff is definitely different.

Comes to mind off the top of my head:
Motor mount pads. 72 are flatter/prone to crack. Mine are cracked on my 72, the 77's are taller and have an extra "leg" for support.

Rear bump stop brackets. IIRC, 77 is larger bolt pattern but look identical.

If your 78 had an in frame fuel tank, the brackets/crossmember may be just a hair different.

Emergency brake lines run through the crossmember on the 72, 78 will have them on the drivers side below the framerail.

Sway bar is different between the 2. The 78 may have rivets where the bar mounts on the frame under the core support crossmember and vise versa.

Brake lines are routes different. 72, proportioning valve is horizontal and I believe outside the frame. 78 should be verticals and in the frame. I may be confused though, but there is a difference.

I believe that is it. I can't think of any other differences.

72-93 are virtually the same

Fuel tank for 72 was in cab only. Brakes were drum in 72 front and rear. Beds mount the same 2 and 4wd. E brake is different. Wheel bolt pattern for 2wd is 5x4.5" till 84.
Wheel bolt pattern are as followed

W series-PowerWagon-4wd
72-74 5x5.5"
Late 74-79 5x4.5"
80 up 5x5.5"

D Series-2wd
72-84 5x4.5"
85 up 5x5.5"

Another way to remember the 4wd Bolt pattern is The full-time is the only 4.5" bolt pattern.

If you plan on running the saddle tank swap the required crossmembers needed.
Sway bar was 1 yr only also in 72

My 72 D200 has discs in front....

Most likely converted or mid late year upgrade? Ive always heard 72 was drum. Know of one for sale even

D100
RAYBESTOS Part # 1924R {#101924, 1924} Professional Grade; Outside Diameter 12.62" / 5 Bolts / Not Finned
Front

$80.99


D200
RAYBESTOS Part # 1982 Professional Grade; Outside Diameter 14" / 8 Bolts / Not Finned
Front; 12" X 2-1/2" Brakes [Wholesaler Closeout -- 30 Day Warranty]

$25.34

They also show a Rotor for both

My truck is a later build, not sure on the date, but the partial Vin is D24BF2U581***.

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My 72 D200 has discs in front....

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Most likely converted or mid late year upgrade? Ive always heard 72 was drum. Know of one for sale even

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Discs were optional in 72 but they use some 1 year only parts.