The CVD bones for RS4 kits will fit the CVD axles for RS4 kits (and there is crossover between many of the other brands as well - for example to make Super Nitro CVDs you can use B2/B3 CVD bones and Nitro RS4 CVD axles), however we've never had too much of a problem with the Pro 3 bones coming out of the diff outdrives.
And for the record the bulkhead dremeling wasn't my idea (I wish I could take the credit for it), one of the Japanese racers did it first.
Also - don't dremel it too much...if you are in a "no one-way" race like the Reedy TC race you will get belt slippage. However, the Losi guys used the belt as a slipper clutch at last year's race, but it tears up the belt - this method isn't recommended for anyone who doesn't want to replace their belts every several runs.
The spacers under the front bulkhead plate idea (a picture from the HPI Japan site is posted a couple of pages back) is only for the HB graphite plate chassis - it does not have holes large enough for the small flanges that surround 3 of the bulkhead plate screw holes. I'm pretty sure the primary reason for the spacer is not to loosen the belt.