Easy- - - - -c-clamp or wire a 2-foot piece of 2X4 to the pad of your floor jack, and use that to position the door where it needs to be. I've installed bunches of them that way when I was running a 1-man body shop. There are professional tools that do the same thing, but I was on a real shoestring budget. When it was necessary to get a job done, out the door, and paid for so I could go get a burger at the local greasy spoon, it was a real incentive to produce!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!