very strongly agree with Piet.
once the oil has drained to the sump, by gravity from all points of the motor, it has to "flood" into the inside of the (stock) mesh filter, from the height or depth of the sump capacity, although inside the filter will be under (a little) suction from the pump, I doubt that a paper filter will allow enough oil into the chamber fast enough, then the pump will not have a puddle to suck from = DISASTER, the oil pumps on stock SOHC 750's are already known to only provide marginal lubrication, if the bike is at idle for any lengthy period of time, what you are proposing will make this a lot worse, my own (at the time) 2 year old 750 suffered "squared off" cam lobes at 23,000 miles due to a lot of city riding.
Again, as piet, install the filter (if you must, there is no need) on the postive side of the pump, this is a stripped motor/ empty crankcase job, involving drilling tapping, plugging, machining, and even (depending) alloy welding. Not a task an average DIY'er would be able to do successfully, it is possible though and has been done.
paper filter in sump? .....Dont do it!
if worried, strip the motor, clean everything, including internal oilways and the crank slingers, measure, new piston rings, grind valves, valve springs, seals, gaskets, rebuild, and you will get 100,000+ kilometres from then, even if the original stuff (pistons, crank, bearings) OIL PUMP!!! is within wear tolerances.
CLEM