Need manuals , what to buy, help with #s

The tag you show is on the engine, right? So that is the serial number for engine and should match the chasis serial number if engine is original or someone took the time to make a new one or swap the old one over. There are some differences according to serial numbers, so probably best if the original serial number on the engine is left as is even when put on a different chasis.

Toggle switches may have been for a lighting system. They are not needed just for the charging and starting. The generator and regulator do not require a switch. When generator armature voltage drops, the cutout relay in the regulator should open to prevent discharging the battery through the generator windings. So if you shut it down, or idle the engine, it should not go dead unless you have something like lights turned on.

Yes, Should be one on the right side of the engine, and one on the rear housing below the fuel tank. Yes, if it has not had an engine swap the numbers will match. The D2 5U has a D-311 engine. Engine servicemen's book is separate from the rest of the chassis. Parts Book, and then the D2 servicemen's book covers the drive train repair. Any Attachments ( Like a Blade.) would have its own books also. I have some 5U Books in the For Sale section if you are interested. Dandy Dave!

In his first post he found 2 serial #'s and at first thought that they were different--but then figured they were the same---different posts on the same subject tends to make it a little more confusing for others to follow. It appears that the engine is original.