To wrap up this thread...
The engine had to be torn down almost in its entirety. The post-mortem revealed two scorched cylinders. Have a look.
https://www.dropbox.com/scl/fi/rw0legofd1cft8nz47foh/piston-1.jpg?rlkey=w7lyiy87b1cnlim5rgau52to5&st=micxurew&dl=0https://www.dropbox.com/scl/fi/b9cd855scshjoy7cz70p8/piston-2.jpg?rlkey=0gsyuq7lyxag517qndapb22s9&st=6dti1m1f&dl=0Nearest they could figure the connecting rod on one of the pistons was bad. So the engine was doomed from the day it was delivered.
Sidebar: I could not return the long block because the mechanic who did the job took so long the warranty expired. So a new mechanic took over the job and had difficulty with the engine (well documented here) even hiring an outside expert who thought he had found the problem, but, alas, had not. It was not until the final teardown that it was revealed the root of the problem deep in the long block.
Everyone was losing money on this project, but, I think, everyone wanted to see the boat back on the water. Hence the final rebuild with new connecting rods, pistons, fuel injectors, etc. Now the boat flies on the water as if it were new. Here it is docked at Matia Island, Washington a week ago.
https://www.dropbox.com/scl/fi/a2mx25emtv1l7dx9kfp26/IMG_7732.jpg?rlkey=3ygqb1yp6iarluytwapiktd0l&st=hj197rwt&dl=0While I have a new engine I must say that its two+ years in the care of mechanics who took their time also took a toll on the boat. It sat outside almost the entire time. The gelcoat suffered some oxidation which needed six (yes, SIX) passes with oxidation remover and polish just to get it to look half-way decent again. it will probably require six more, but my arms are tired. Also, as the boat was left mostly unattended through rain storms in winter, water leaked in under the cockpit cover and now I am looking at wood rot in the cockpit floor above the fuel tank. I am handy enough to have MacGyver'd a fix for the sagging plywood cover (added some shims and more to keep the floor even) and will set out for a more permanent rebuild of the frame around the gas tank in a week or so. The rest of the floor looks okay. I don't see much of any advice on floor repairs on Sundowners in this forum, so I'll post what I learn.
Despite the neglect from the shops, the vinyl is great, and the fiberglass looks fine (faint cracking of gelcoat at window joints starting to appear - not sure that's an issue yet).
Oh, and the trailor took a beating in the weather outside. That's for another post.
Thanks for your input along the way.
Mark