"....turned on the water, got the exhaust water just sputtering along, fired it up ..."
I highlighted parts of the quote in hopes that the sequence you posted is wrong. Get your plumbing ready, but start the engine FIRST.....THEN turn on the water. Water first is how you get water in the oil.
All the trailers I've had are a 5 on 4 1/2 bolt pattern with 1/2-20 studs.