#1
See title

Can a pickguard off a Gibson Les Paul Standard be used on an Epiphone Les Paul Standard? And vice versa?
#2
yes.
Gear:

Gibson Les Paul Vintage Mahogany

Epiphone Les Paul Goldtop with Seymour Duncan Alnico II's

Seagull 25th anniversary Mahogany Edition

Crate GT65

Digitech Metal Master

Dunlop Original Crybaby Wah
#4
They should be Ok. If there is any variation it would only be like 1-2mm. I took my Epi LP custom pickguard off and put a Gibson LP Standard pick guard on and the differance was only 1mm. So you should not have a problem.
If you start a reply with: I have never played one but I have heard good things about it! Your opinion is invalid.