The BW35 trans is a heavy pile of crap. That's most of the problem, and the later B30's had lower compression as well. If the distributor has a vacuum retard capsule ( I think it does ) then disconnect it and plug the fitting at the manifold. Crank in as much timing as you can, starting at 10 BTDC at idle. If it doesn't ping keep going up.
I had a 73 164E five speed for a while, and after re-ringing the engine and sticking a new E cam in it, it was a blast. Actually quite quick, and always smooth.
Volvo D-jet pumps are the same really - someone might offer that they have different part numbers or something, but it will not matter. In fact the Datsun pump is a very nice copy really - although Datsun copied the L-jet, not the D-jet. They were smart.
If the throttle switch is in adjustment, then the idle mixture potentiometer will adjust idle mixture. Right rear door, look forward under the front passenger seat, and you'll see a large plastic slotted knob in a metal box. Turn it (works in reverse) to set the mixture. When the engines have good cams and good injector seals, they will idle nicely.
Good job getting it running! Save your money for gas though....