When fitting a higher compression or larger displacement motor to a 600 chassis, there are a number of options.
1. Use the A112 pump and an electric fan.
2. Use an aftermarket pump (PBS) and an electric fan
3. Use an electric water pump and electric fan.
If you are using an 8 port head with dual webers, then you will likely use the front mounted radiator. With all of the above options I would recommend using two small electric fans as well.
As far as clutches go, I have used an 850 flywheel (or an aluminum one based on it) and an 850 pressure plate for my race car for over 10 years without any failures at all. I simply mount a 600 ring gear on it. It does require the adjusting the location of the throw out bearing, but once done this is a reliable option. This uses a 160mm friction disc and pressure plate. The A112 pressure plate and flywheel did not fit the Fiat 600 bellhousing, but I have been told that it will fit in a Seat bellhousing. Apparently they are slightly different. The key to clutch longevity is to make sure that the step between the friction surface and the pressure plate mounting surface is maintained.
Hope this helps. If you would like to read more, check out my site at
www.scuderiatopolino.com. Lots more information and parts.