Look at it like this: You wouldn't be "remodeling" your current one you'd mainly be using it for parts. At that point see what makes the most sense for you.
Can you weld aluminum? Its going to require it.
Roof: cut/extend the framing, new roof sheeting, new interior headliner, and need some matching or all new trim that goes around the perimeter.
Sideliner: new sideliner
Camper: Cut and extend the main cabover beam (the weld will need to be of structural quality), depending on the beam calculation you also may need to beef things up so the vertical profile may need to be increased, are you going to add on the top of the whole camper frame or build the beam downwards (which depending on cab clearance means raising the bottom of the camper), also the older camper frames seemed to be mainly 1x1 and framing was much more sparse versus what the newer ones are being built with (more members and also 1x2s are used in more places too) so the frame supporting your current ~32" cantilever may not be up to snuff to support a 60" canilever so additional material/welding/labor to overhaul all that too. Again new or matching trim around the top perimeter, more matching or new siding, etc.
On the beam 1 single 200lb person on the 32" cabover simplistically would have their mass centered at 17" so the moment at the front camper wall (where its the greatest) is 283ft-lb (spread between two beams). With at 60" cabover and lets say two 200lb adults centered at 15" and 45" you're looking at a 1000ft-lb (spread between two beams). So simplistically you're quadrupling the stresses on that cabover which in turn it puts back into the camper frame. I don't know the profile/thickness of that beam off hand.
