Mount it to the chassis and run it hard for several hours. If the thing stays below a "reasonable" temperature, you're good. If the rectifier gets too hot for your own comfort (or too hot to continue functioning), then you needed a heatsink. Add one and try again.
Without giving more detail, that's about as good an answer as you are likely to get.
that quarter inch ally plate is a large heatsink and lots of inertia to cope with peak loads.
I'm No.3 that thinks you will be OK.
Have you tried to calculate peak currents, at start up and running?