Carl
Don't even think about a pallet truck.
As you surmise the close coupled pair of swivelling wheels at the handle end make things very unstable at the slightest provocation. I've seen a Bridgeport overturn off a pallet truck when a turn was attempted on less than perfect ground. Very impressive bang. The mill appeared to survive but i didn't give it a close inspection and it was on its way to auction anyway.
A pallet truck is possibly acceptable on a smooth, flat surface with wide sweeping turns but nowhere else.
When I moved mine I bolted sturdy timber H sections under the ends of the table and adjusted things so they just skimmed the ground. Inch or less clearance. So if things started to tilt the machine couldn't go very far and would sit at a stable, small, tilt whilst figuring out what to do next. Turned out to be a good idea when mine, not unexpectedly, tilted towards the lawn where the path made a right angle off camber turn. Having already laid a sheet of plywood "just in case" supporting things level whilst inching round the rest of the turn was simple pry bar exercise. The plywood suffered.
I shifted mine on a self made, super heavy duty dolly having a frame of 2 1/2" x 1" alloy bar with 4 heavy duty castors having 2 1/2" diameter by 2 1/2" wide wheels. Probably good for 3 tons or more. The small diameter wheels kept everything reassuringly low to the ground.
I took the head and ram off separately before moving which made a big difference. By far the easiest way to deal with the head is to arrange an R8 arbour on a stout foot that can be bolted to the table. Fit the arbor into the spindle then bolt the foot to the bed. After removing the bolts use the Y feed on the table to draw it off. Bring the table down to a sensible height and lift off. Reverse procedure to replace head when the mill is where it needs to go.
If you don't have a hefty dolly I've found that laying steel rod or stout, small diameter, pipe down rail fashion and sliding the machine along works much better than pipe rollers or skates. Especially if the surface isn't particularly good.
Clive