Thanks. Merry Christmas. But that does not answer the questions asked. Full rebuild is the default to repairing a faulty transmission, as is replacement...which isn't the question. So...returning to the big picture and goal of this thread,
the goal is to determine the health of the engine and to keep the car mobile, which can't currently be done. Now it's only mobile. Doing so without spending $1000 to $1500 on a trans that won't be used in the swap that I mentioned in the OP is the goal. The engine can't be tested in boosting phase presently. And it makes little sense to just take a gamble and build a complete Fiero swap based on this untested engine especially when it will be mated to an F23 trans and not an automatic transmission. Thus spending $1000 to $1500 to rebuild an unused transmission is not a practice in sensibility, but I am on a Fiero site so maybe I'm being unrealistic.
Perhaps the engine loses oil pressure when warmed up? Maybe it smokes when warmed up? Maybe it consumes copious amounts of oil, or even anti-freeze? These are some of the goals of this exercise.
However, since trans diagnosis seems to be of greater interest currently, I'll add that I trust the diagnosis of
the mechanic 
who owned/sold the car and am not arrogant enough to dispute him. The person he got it from brought it to him because he thought it was a CV shaft/coupling getting worse, since it sounds similar. When he got the actual diagnosis from
the mechanic , he traded the car to him due to cost of a rebuild which would be more than the worth of an ugly car that he commutes in for 80 miles per day.
The mechanic , who became the owner of the car determined that the car has lost half it's factory GM paint, which is common to white GM cars of this vintage, observed that it also has an aging interior and knows that there is no profit to be made from repairing/replacing a trans in a car needing a complete paint job, that won't sell for $1000 when fixed so he sold it for $650 (his determined investment/plus diagnostic cost) to someone who might want the engine for a project. Hopefully this will satisfactorily convince those curious of the health of the transmission that enough information has been offered so that advice can be given on how to proceed in getting to a point where the health of the engine can be determined?
After more creative word phrasing in search engines today, I believe I have gotten as far as I can get on the internet by confirming that yes the stock chain/gears are weak and prone to stretching when abused and can be replaced, but flushing the old trans can expose other problems that weren't apparent before the flush. It's a case by case basis whether it will be a successful temporary fix. I was hoping to hear from someone here who has experience, but I located some discussion about it on a GP site amongst guys who have had chain failures with modded/somewhat raced GPs. I'm going to give it a try and see if I can get the engine into boost for a period of driven time.
Merry Christmas all.
