Typically you would just rebuild
the existing pump, complete kits can be had for less than 100.00 usd. Don't know where you're located, but if you need a new pump (sometimes they can't be rebuilt) the Volvo
P/N I found is 829825. There is a new one on ebay at this moment for 349.00, There is a new one at 877-621-2628 for 375.00, or you can try Depco in Florida
at 800-446-1656 (these guys have good prices on repair parts
, knowledgeable and helpful too).
These pumps are usually made by an outside vendor for the engine manufacturer, Volvo typically uses Johnson pumps, so if you find the actual Johnson p/n (which may be stamped on the cover plate), you might be able to find it for less than 350.00....
At least one of the problems with using an electric pump is that the output is constant, with an engine driven pump as the rpm
increases, the pump output also increases.