I see lots of the newer trucks with bad motors for sale cheap. Has anyone swapped a older mechanical 855 into one of these reasonably? I realize the dash might be hard to make work.
Most of that depends on the brand of truck, all though it can be done.
Take all electronics out the dash and rewire with some from Auto Meter and keep the ones you can, if you are handy with welding, riveting, wiring and fabricating it can be had. This here "Mystery Ship" been rewired from cab back, some up front, mechanical to digital on speedometer, was 5 speed now a 6 speed, has ability to lock all the wheels on parking now instead of just the transmission that it had. Even tossed the bench seat for air seats, so it can be done with time, just don't bite it all off at once.
I would think this conversion is going to depend on how many other modules in the truck need to communicate with the engine ECM. A few years back I had to fix the mess somebody created by converting a 3406C to a B, the engine was done right, but the speedo and tach had to be wired direct. Trying to convince the customer that cruise control would never work again was the hardest part of the job. Of course the Jakes, fan control, and even some of the air conditioning functions went through the ECM too.
Gayle had a 379 Pete with a 60" flat top and a 3408 in it from the factory, after she let go for the second time he yarded it out and installed a 550 Cat 6TS engine with a 18913. He had it wired up and done in no time.
He was telling me about that one back in September, sounded like a real success story. Got a local that has a junk Volvo with a nice 450HP 3406E that he wants to put in an older Pete to replace a B model CAT, he's going to round up a stand alone engine harness to do the job if we decide to do it. Lots of aftermarket stuff out there for those conversions.