I installed my DW 200 (S), in the oem position. No problem except their strainer would not work. I used the oem style rubber boot on the bottom and clocked the pump for a Napa #B-0052-S strainer. I installed the strainer in parallel w/the float. Possibly, the 300 series would work the same. I did not alter the fuel sending unit in any way.
I will see if the idle problem is going to straighten itself out. It is much better. Too bad I can not drive the car.