I do believe there's a huge difference in payload weight and hitch weight ratings on the pictures old biscuit posted but I'm still not for g-neck adaptors on a 5er. Just the duallys on the g-neck trailer are a dead giveaway it's not even close to a fair comparison. I did serious damage to one of my 5ers with a g-neck. The adaptor doubled the distance the front of the frame flexed and it tore up the siding and wall paneling. But... if it doesn't have any damage by now it might be worth a chance and I'd get that adaptor off ASAP. Hopefully your friend will level with you if he knows of any damage. Craig