Hello, everyone; just thought I'd do right by y'all that have taken the time to assist me and give an update (ChrycoPsycho, glad to see you saw my "I'm adrift post" also):
Well, 4 speed fish, just as you predicted / guessed, whomever dropped the 440 in my originally 340 car FAILED to also install the correct size (OD = outside diameter) bearing retainer at the same time.
I measured it last night and, the center bore size of the center opening in the bell housing that came with the 440 is inside diameter (ID) of 4.80.
Conversely, I measured the bearing retainer on the still original-to-my car tranny and it is OD 4.35"
Not surprisingly, that .045 difference between the OD of the retainer and the ID of the bell housing was plenty enough "slop" to ensure the end of my 1" / 23-spline shaft would get boogered to h*ll and destroy the pilot bushing.
Also, and as recommended, I called Wayne at Brewers this morning and he consoled me (somewhat), "Thor, we see this ALL the time."
To add to my sorrow, it now *"appears"* (so far) that everything inside my original tranny (gears, etc) may not have been non-damaged yet and that I caught this whole thing early on enough (but, who can really say for 100% sure).
Bottomline: I am left with a 1"/23-spline input shaft that has an end that's boogered out-of-round.
From what I'm hearing, "Good luck finding one of those" and "Even if you do, after (competent!) labor, etc., you'll be tapping on the doorstep of the $1,299 Brewers can send me a 100% good replacement tranny for."
At this point, I'm inclined to order and install the replacement tranny from Brewers and hold onto the original-to-my-car tranny and worry about options for salvaging it with a replacement shaft later, down the road.
I sure want to thank everyone here, this saga obviously ain't over so, please keep the feedback, input and experience coming (I respect the h*ll out of what each of you has gone through for that experience!)
For instance, I need to ask Wayne if the replacement tranny they send me will be 1"/23-spline shaft with the only 'modification" being a 4.80" bearing retainer or, are they going to recommend I go up to a 1-3/16" / 18-spline shaft . . . (and, obviously, also clutch) . . .
And, 4 speed fish, I now have you on speed dial! ;-)