Whoa! That poor heatsink :P

As for the PSU mod; I'm not sure where to get 16 or 18 pin Molex-type connectors that would be keyed right for this board. I would recommend using the connectors from the EPS adapters you already have. If you're up for it, pop the PSU open and de-solder everything from the ATX harness except the 3 +12v lines, 4 Ground lines and the Power-ON line. The EPS adapters will use the same pins as the ATX (20/24-contact) and P4 (4-contact) connectors so you can either use a pin extractor to swap the lines out of the defunct ATX connector, or cut and splice. Do the same with some 4-pin Drive connectors for extra +12v lines. It's probably safe to have only two +12v lines from the PSU actually going into each 8-connector block; just get some appropriately-coloured 16 or 18-gauge wire and run splices between the pins so they're all powered. If you want the connectors to look more streamlined you could just crazy-glue them together into 16-pin and 14-pin blocks. I'd recommend leaving the last 4 pins on the 18-connector block empty since they're not documented right now. Wire the Power-ON line and one Ground line into a connector like This and install a conveniently-located toggle switch in your case with a corresponding plug and you'll have a power switch!