Mixed Company -300D Tranny transplant

[Barrelhouse]

Some time back I purchased a 1980 300D in great shape with a seized up engine. I was assured by those that I trusted to know about these things that the excellent engine from a 1977 300D could be transplanted into the 1980 car to complete the restoration.

The engine swap went reasonably well but now I am getting stories of bizarre adaptations that I originally was advised were fairly straight forward. All involve the vacuum controlled transmission that had to remain in the '80 car. Some of the guys in on this forum stated their preference for one tranny model over the the other, most in favor of the non vacuum model while others held them in equal regard.

It has now been suggested that the adaptation is virtually impossible because of some component the negative technician made sound like was the size of phone booth. A modulator I believe the fellow said. Another less factory trained tech says the modulator is actually the size of a pack of cigarettes in most cases and could be installed in any number of places. He explains that it is there to prompt the transmission to shift. So, I guess we can't just hurl it out the nearest open window.

The engines are said to be identical for the most part and the '77 seems to have matched up to the transmission . . Anybody with input will be appreciated. I found vacuum diagrams for the '80 and will take them to the mechanic that now has the car. Digrams for the '77 seem more elusive but suspect the Haynes manual may explain. . that and the engine is right there for all to see.
Thanks,
Barrelhouse