how hard is it to put early 240 bumpers on a 75 280?

NO IDEA, but if you want to sell those bumpers let me know.

i'm interested.

You have to make your own brackets, but its not hard. the hard part is actually removing the old rear bumper and bumper shocks. I'm in progress of doing this now. I've got the front bumper mounted and perfect. I'm in process of removing the rear hardware now, got one side done and am dropping the tank tomorrow. Just do a search for "240 bumpers" or 240 bumper swap and you will see plenty of posts.