[dad911]

Lay the door on a pair of saw horses, Clamp the jamb perpendicular on top of the hinge side of the door, and either use a square to transfer the hinge lines, or use the hinge itself.

Then set up your neighbor's jig, and whip the router around......

I would probably build the frame around the door, then hang the assembly like a pre-hung door.

Or you could leave the old frame in place, veneer the jambs and just replace the trim.