Another interesting (to me at least) note about timing. If using your manual advance lever does improve the way it runs, then that is probably a clue that a timing adjustment will help you get more out of the motor... remember that that manual timing adjustment only bumps the engine's base timing at the bottom of the RPM range, and by about 2500 RPM it is no longer having any effect at all. The advance lever works by rotating the roller cage inside the pump a certain distance to make the injection begin sooner, but its range of movement is much less than what the pump's pressure-controlled dynamic advance system accomplishes as RPM rises. Even at its furthest point the advance lever only can move the cage to about where it gets to anyway by ~2500 RPM thanks to the dynamic advance piston moving, and beyond that the pump just reverts to its normal advance curve with no further alteration regardless of the position of the manual advance lever. Of course, 2500 RPM is right around where the turbocharger begins making boost, so any improvement effect that can be achieved by using the advance lever is unfortunately limited to the part of the rev band where the engine is hardly to make any power anyway.
The electric high-altitude advance solenoid used on the later-model Volvos has a slightly more thorough effect on timing, since it works by altering the pump's internal case pressure and thereby shifts the entire advance curve rather than just altering the bottom half of the curve like the mechanical advance lever does, but ultimately it too is limited in its effect because the total advance capability in the pump still tops out in the same place, determined by the end of the range of motion of the advance piston and roller cage. The only way of really shifting the entire timing curve one way or the other is by changing the pump's basic timing setting.
Getting "reasonable power" while keeping smoke at a minimum should be an easily attainable goal once everything is in adjustment. It will probably never be a rocket but getting up to highway speed in under 3 minutes should not be a challenge at all even while hauling such a large and heavy van... a 3500lb Volvo can do it in less than 15 seconds without breathing too hard so I wouldn't think yours should take much more than a minute at the most. At least on flat ground... if you're merging onto a highway uphill at 8500' then my bets are off.
