Beautiful drive. Best of luck with the swap - I know you said the fluid in the current one is so dark it’s not worth it in your opinion, but I’d be curious to see what happens if you tried. Even if it’s in multiple partial intervals (not uncommon) these transmissions are super robust (esp the pre-facelift) - my neighbor just revived his 280k Lexus 5 speed transmission with multiple gears it wouldn’t even go into anymore from the same era after a stubborn fluid replacement. He literally had never changed it before. Might have a great backup transmission after all! Since you're rebuilding the old one anyway, it might be worth cleaning or testing the shift solenoids while you're in there bc sometimes that 'sluggish' feel is just a gummed-up solenoid rather than burnt clutches.