Matt, too many questions for one old brain
I think the white powder is what results when gasoline with ethanol separates after sitting for awhile and the ethanol then combines with water and finally evaporates...t
he white crap is left behind as the alcohol and water corrode the surfaces the mix was touching.. Note, I said "think". I have seen it before in carbs and such.
As far cleaning it up, I have not seen anything advertised for the problem. I guess I would start with fresh gas and see if it will lift it. In the old days, radiator shops had stuff to clean out as gas tanks. I know you can buy coatings that you pour in and slosh around to seal rust, etc. in the tank but I have never used one. A new Spectra tank is about $150 from Rock Auto and a new, or a better used tank might be the best solution.
I would suggest reverse flushing all the lines. Ed may have a better suggestion than gas. The injectors are going to need cleaning for sure and even more so if there was no filter on the car...some times things are just unbelievable. Blow some gas thru the rail and hope you get the rust, etc out of it. You might talk to Chuck Leeper (The Ol Buzzard) and see what he thinks about cleaning stuff out since he is the injector cleaner and a lot smarter than me. Drop him a pm and ask him his thoughts
Yes, the filter is in front of the rear tire, drivers side
http://www.vortexbuicks-etc.com/fuelfilter.htmlYou will probably have to buy the Dorman fuel line repair kit which comes with 3/8" tubing to fix the hack job.
No, the two connectors do not plug together....Th
e one with the green connector (was thinking it had two white wires) is the tach test connector. You can connect a tach to it. The other connector should have a gray wire on it and if you put 12 volts to it, the pump should run. Normally it would run the pump in the tank. Given someone butchered this one, it may, or may not. The green tach connector has a tach signal on it and should not run anything.
If you can get the oil cooler line off, take the one that is marked "To oil cooler" in the third picture down on this page
http://www.vortexbuicks-etc.com/frontcover.htmPour oil down it back into the adapter until it will not hold any more. This should fill up the oil pump so it is primed. Take all the spark plugs out, squirt some oil in every cylinder to try to lube the cylinder walls a bit. Disconnect the orange ecm memory connector before you crank it. Also, take a new oil filter, pour as much oil in it as you can, and then spin it on so you have a full oil filter. Do all this before you crank the engine over without the plugs in it. This should start the pump pumping and get oil going thru the engine again. If you don't quickly see oil pressure, do it again. The reason you disconnect the orange ecm memory wire is to keep from hurting the ignition module which can happen if the plug wires are not connected to the plugs which have to be grounded as well....Normal
ly there is no need to mess with the cam sensor altho some might say it was a good idea on an engine that has not run in years....being you have already cranked it over, I am not sure it makes any difference. Your technique sounds right to me if you go that route
Reconnect the orange wire when you are finished.
I would change the oil...no sense pumping oil contaminated with water thru the engine. I might even put a can of EOS in the oil to try to give the lifters a break to minimize scrubbing on a dry start.