@ JT - the recommendation to use Lucky Bob's acid flux has made all the difference in getting cleaner solder joints. Any excess is just filed off and sanded with a 1500 grit stick.
Installed a Scalextric Sport slimline 25K green motor though I'd prefer the 21K red one which is pretty hard to find these days. Gears are a BWA 9t pinion (another NLA) with a Slot It 27t crown for a 3.0:1 gear ratio.


Test ran it against my older Cheetah build 2 on my twisty 3-laner and was pleasantly surprised.

Got a fastest lap of 5.662 seconds vs. 6.213. That's significantly quicker but you've got to consider the lighter weight (70g vs. 83g), higher rpm motor (25K vs. 21K) and freshly sanded and trued tires.
Ran a stock Slot It Mazda 787 run right after and best I could do was 5.922 seconds. Really good outcome to better a Slot It car.
Onto some modeling detail.
Dan