My two cents. As has been said, most Old RV's can be restored. The ones that can't are too far gone for much else the scrap metal, and at least around here that can be a lot more costly than beneficial.
The 454 should be able to get running with only 60k. I know I have two. Both are 1987's. The biggest issue on old engines that have sat is the rubber, and synthetics on the engine and related parts. Just keep in mind a lot of guys have made many RV's out of busses a lot older. Some are pretty cool, just depends on your skill level or how much you are willing to learn along the way.
IMO, only YOU can determine if it is "worth it" to YOU.
Keep in mind that you will never get your money back by selling it. No matter how good of a job you do, it will never be worth what you have put into it, especially if you keep track of your hours (at $50 per hour), and take into consideration any sub-contracting you may have to do.
If you are rebuilding it for your own use, though, "worth" is entirely up to you.
CM1, USN (RET)
2002 Fleetwood Southwind 32V, Ford V10
Daily Driver: '06 PT Cruiser Turbo
Toy: 1999 Dodge QC SWB, Cummins, 5 speed, 4X4
Other toys: a pair of Kawasaki Brute Force 750 ATVs and a boat.
"When seconds count, help is only minutes away!"