does anybody know what the RPM limitations are on an 1987 alpha outdrive?

There realy is no RPM limit for any drive, they all have power limitations to em but not RPM's what Rpm are you looking to turn one at?

I had a 86 Wellcraft Nova with bbc, headwork, hirise, 810 holley, CMI's through a original alpha (1:32 stock ratio) spinning a 23 hydromotive 3 blade at 5200 rpm all day long with no fast start blast and drive held up for over 150 hrs & 18 years...very happy til the day I sold...always used syn gear oil...vessel was plenty fast for me

been spinning mine 6000+ for the last few years no problems, hopefully towards 6400-6500 this year

I was only talking about like 5500 so I guess I'll be fine

5500 is no problem at all.