Re: time to paint my outboard...
I'm using Kleen-Strip Strip-X Stripper from Wal-mart to strip a '57 Johnson. It's pretty much off-the-shelf stuff but it's working good. It immediately removes the Dupli-color junk somebody put on it, the original paint underneath with a little more effort, and is not affecting the green zinc chromate primer hardly at all. When finished, I'll finish sand it, wash with TSP or Tide, spray with etching primer, and spray with single stage acrylic enamel. That's all the exterior and any internal parts that I remove (starter bracket, recoil starter, etc).
The powerhead itself is so intricate, I'm not sure stripper or sanding either one would be successful. For it, I'm planning on cleaning well with kerosene, then with Tide or TSP, maybe rinse with vinegar solution, then a final wipe/rinse with laquer thinner before priming and painting. It probably won't last another 50 years, but my kids will sell it long before that.
That's the process I used on a '56 Javelin last year and it turned out great.
I'd be afraid of oven cleaner. It's high alkali and would eat aluminum like a dog eating hamburger.