The best way I have found to center the nozzle in the burner tube is to weld three nuts at 120 degrees, with holes under the nuts.
Then put a screw in each nut/hole, and adjust to get the nozzle perfectly centered in the burner tube.
You can operate an oil burner on diesel outside the furnace, and if adjusted correctly, it will operated outisde the furnace.
Most burners do not operate well ouside a furnace.
This was an early diesel burner; the first diesel burner I built.
Typical oil burner uses somewhere between 1.5 and 2.7 gallons of diesel per hour, depending on your furnace size.
Using excessive fuel will cause the furnace to operate at a lower temperature.
I use a variable speed Toro leaf blower set to its lowest speed for my furnace.
You could get away with a shop vac output for your size furnace, or perhaps something even a little smaller.
This was the lastest iron pour I have done, which has been a few years ago, since my workload went way up in the last few years.
This was sort of a whimsical pour, and it was an art-deco plaque of sorts, of what is suppose to look like a Phoenix, in gray iron.