As I posted in the newbie threads, I have a 2.4 that certainly has some internal damage due to a timing belt incident.

First: the 'confession', and what I learned from the experience (might help someone else):

my 1990 D-50 blew smoke on cold start-ups. This eventually prompted me to add Lucas oil...very thick. In the cold Virginia autumn, it was slow to crank over. One day while warming up, the timing belt chewed some teeth.

What I learned:
The cold-start smoking was likely from worn valve seals. I suspect that when the engine was turned off, and sat, oil leaked from the cylinder head into the cylinder, awaiting the time to be burned. Once the motor was warm, smoking was minimal or non-existant.

My Chilton book on the vehicle gives wonderful instructions for cleverly replacing the valve seals without removing the head: each cylinder at TDC, then stuffing nylon rope through the spark plug hole to support the valve after the keepers are removed. I didn't know that, then

And now I have a 1989 D-50 I bought from a neighbor. Their report is that it sat due to a suspected head gasket breach. If I gauge this from the inspection sticker, that truck sat for 12 years. BUT...it isn't a broken timing belt, so the motor is in a state of preservation.

'89 forensics: No water in the oil, but #1 & 2 spark plugs were excessively fouled
The timing belt, though intact, is seriously in need of replacing.
Precautions I took: Before moving the vehicle, I added a gallon of fresh fuel and some Seafoam so it could slosh around on the tow to my home. I then drained tha tank.

I also made no attempts to turn the engine over. I added a whole can of Sea foam to the crankcase, and upon getting the vehicle home, drained the oil and removed the filter. Fresh oil and a new filter, with spark plugs out, I hand-cranked the motor several revolutions.

I asked about using the head from the 2.0 for the 2.4. I am interested in the other possibility:

Can I put the 2.0 (complete, with new timing belt) in the fuel-injected truck, and the 2.4 sensors adjust it to the lesser-degree in fuel demand? If so, this would be awesome, giving me a motor (and transmission) with 60,000 fewer miles. It allows leisure time to rebuild the 2.4 (and locate a head for it...or use the existing one after reconditioning).

Having both trucks has given me some great possibilities, though i think I do not want to retain carboration in exchange for fuel injection.

The '89 will be a parts truck. Though I thought of making the bed into a trailer, at this point in my addiction to D-50's, I refuse to hack up a vehicle that becomes rarer every day that passes by.

Any and all comments are humbly welcomed, and expert advice is really appreciated.