Based on how good that Mercury looks Tim, Id say you are doing him a great favor just setting an example in perseverance already.
He can realize for himself its time to cut losses, get the trans moving and prep it for sale. Somebody who is all about body work would recognize the value of having all those mechanical items already addressed.
Does he have an idea what he wants as a replacement?
My dad had a very utilitarian view of cars and I was not permitted to buy anything over 10 years old with over 100K miles. My first car was a 1973 Fury cop car, an emissions-control disaster. I had to learn everything about carburetors, intakes, exhaust etc by helping neighbors and friends. My second car was a 68 Mustang with a 289-2V, totally appropriate for an 18 year old.
Most of us who started driving as the big 4 automakers were cheapening, downsizing and basically experimenting in awful ways making cars ugly, which took decades to reverse. We revered cars from the pre-1975, that ran on regular gas and had vacuum hoses for only necessary functions. Unfortunately, the older dudes that had the 1950s-early 60s cars weren't letting them go anywhere close to our budgets