Sounds like I'll be making a phone call in the morning!
Got back in touch with my local tranny guy today. After checking with his contacts and supplier, he said the general consensus was that we should be looking for around a 1200 rpm stall speed, 1500 being a little on the high side for where our max torque supposedly comes in (1800 rpm).
None of the people my tranny guru trusts and does business with have done an honest-to-god diesel version of a 545 TC, but then added "you should see one available before too long". Hmmm, I wonder if Suncoast is one of the companies he trusts?
Here's a nice little bombshell he dropped on me - one of the reasons it's so bloody hard to find a 545 TC right now is that a certain company, which shall remain nameless, has been snatching up all the used TC's, doing a quick rebuild on them, and shipping them out to perform a certain recall. And of late, since these rebuilt TC's have been going T/U, has wised up in at least this area and started shipping out new TC's to perform this certain recall.
Another person on the list e-mailed me with the results of their brake stall speed test. He performed it 3 times, and got the same result each time - 2400 RPM!

He hasn't had F37 done yet, but did have the TC replaced prior to this. Considering the dealership which performed the replacement, neither of us would be surprised if they simply half-a###d it and slapped a V6 TC in.
Mine is a May '05 build, and has never had anything other than filter replacement done by the above mentioned guru. At the latest, I'll go out this weekend and do the brake stall test on mine. If it also comes out to 2400 rpm, we can make a pretty good guess as to the truth of the matter - that DC gave us a juryrigged V6 TC.