How hard would it be to put a normal les paul pickguard on one without one?
on a scale of 1 to 10 id say about 0
not hard. you'd have to drill maybe 2 holes for it.
When you drill holes, put a piece of masking tape over where you are going to drill, then drill through the tape. This makes it less likely that the finish will chip.
Don't do it yourself, You might damage the finish, go to a guitar repair man and ask him to drill it on.
There is a reason why TS is asking this in GB&C, most likely, because he wants to do some Gear Customizing...
I thought for LP pickguards, you would need 3. I guess, you only need 2 then.