You nailed it - the gearbox and final drive case are a different paint:
Did the final drive and reaction arm yesterday. The paint on the final drive case is clearly different from the paint on the reaction arm and its mounting bracket. Separated the bracket from the final drive case, applied Crown Tuff-Strip, waited 15 minutes (almost) and 99.9% of the paint came off in sheets leaving clean, pristine, virgin metal behind. The remaining .1% came off with a little fingernail scraping. Same with the reaction arm. The final drive case? What a mess. Same stripper, same time, different result. The paint didn't come off. Turned into sticky black goo that had to be wiped off, not scraped. With difficulty. In small sections. Try to do too large an area and the stuff hardened before I could get it all off. More stripper. More wiping. Lather, rinse, repeat ad nauseum. Got into the recesses with Q-Tips. Took 4 or 5 passes to get it all.
Took 3 hours but I got it clean and it's gorgeous.
Started on the engine today. Crown Tuff-Strip takes the paint off in sheets, like skin off BBQ chicken, leaving clean metal. A test on the gearbox showed that it's painted with the same crud that was on the final drive case.
I may strip just the engine...
Wonder what Tuff-Strip would do to wheels.