Hi Neil;
First, my apologies for not answering your earlier question sooner, but it's been a busy week.
I'm not certain which dimension that you were looking for, but with it in place it is difficult to measure anything but the rotor cup.
Those measurements are 6.3" OD on the cup and after I machined a little off the face edge of the cup I was left with 1.35" thickness. Looking back at my report it looks like I had to remove a total of about 0.156 off both sides of the cup to make it fit so it was probably about 1.5" thick originally. At the time I did this I had detailed notes on every possible dimension, but that was some years back.
Not knowing enough about your PSRU, I can't say for certain which would be a good fit, but from what I can see of the Racemate, while it is a good solution for the purpose in which it was intended as a belt driven waterpump alt, I think if I was to do it again, I would not hesitate to use the Harley style again, rather than pay extra to modify something that is well designed for the other end of the engine.
But I would not buy it from the local Harley shop ever again as I paid far too much for it. I would use the Compufire #55540 kit with rotor, stator & regulator which can be bought at Amazon.com right now for $197.64 usd.
This would be your most cost effective way to add it in and apparently Compufire is manufactured in the USA. (for those worried that it is a cheap Chinese knock-off)
As far as machining costs, once again I do not know the details of your design, but with mine the greatest difficulty was in doing it as a one off design. But if I was to have been doing a bunch of them, I don't think the additional machining would be too onerous, but would not be able to put a dollar amount on that work. And of course, outside of machining and parts costs, you've got to cut yourself a little something as profit for this venture.
Now with that said, to answer your current question if we think it would be worth it, I would say yes. I've been doing a fair bit of ground testing for unrelated issues but as I disconnected my main alternator in order to access oil lines, I've been running on the back-up PM alt only and it is working flawlessly. Even with both working I can switch seamlessly from the main to the back-up with only a slight volt drop of 0.4 due to different voltage regulators.
It seems like a lot of money, but in my opinion it is better money spent than on a back-up lightweight battery. Of course I won't be a customer since I already have it and my opinion is biased, but while I could list more than a handful of things that I wouldn't do again, this isn't one of them.
I would do it again in a heartbeat.
Todd