Agreed - I thought about it several times over during the round trip. However I don't drive it long distances - around here it rarely gets into 4th gear unfortunately. After the other projects I have in mind - lower springs/bilsteins, maybe genuine 14" Alpinas, I will then likely accumulate the parts over time, keeping an eye out for a local donor tranny and source the driveshaft. By then we'll be empty nesters and possibly take it on longer missions.
Your following statement:
('I spent 6 months prepping the car mechanically--it ran beautifully for 750 miles at 4k rpm / 80 mph.")
I toured at the same RPM and speed or greater for years in BLUMAX with a 4 speed while covering over 300,000 miles all around North America. Your statement tells me it's time to seriously consider a 5 speed OD for your car--it will absolutely alter the pleasure of touring longer distances at speed by calming the beast. So equipped you will find travel at 3K will then border on the upper edge of "legal" speed at about 80 mph depending on your diff ratio. Carl installed a 5 speed in BLUMAX in June 1996.
Now over 100,00 miles later it has proven to be the best single improvement to the BLUMAX among the numerous mechanical, suspension, brakes, etc. that have been made over the years.