What's normal running, or recommended max revs or top speed. I've been driving my 3 bearing engine flat out for the last 850 miles.

I have broken three in thirty years all three bearing, two were heavily thrashed in a Paxton special and I mean thrashed the other quite sensibly driven up the hill out of Dover in my Opal.
Why, except for cost would anybody invest all of there cash in rebuilding an engine, and it is not cheap, not fit a modern crank with a record of reliability . There are three manufactures of these that I know about and they are realistically priced. For the "" purist the three bearing engine can have the centre web removed and fit two bearing and nobody would know the difference.

That's my five farthings.