Looking at this situation again, it really is the definitive modern dilemma of amplifiers- How much are you willing to compromise for tone versus portability. There are a several ways to look at it. Is this a collector's amp? Or just a gigging amp? There are dozens of Super Reverbs on eBay, with "buy it now" prices over 2K, for what look like nice, but not really collector's grade amps. A true collector's amp would easily fetch over 2 grand, but most 45 year old amps that have been actually gigged with will show some or a lot of wear and tear- which doesn't mean they are bad amps, but they won't be worth a lot of money. The unique characteristic of a Super Reverb is that it is an elegant design in every respect- tone, responsiveness, volume, size, versatility- any alteration of the design will diminish it- it is arguably as perfect as a Blackface Fender gets. It is heavy, but not for the amount of air it can push. A Twin-Reverb with JBLs is louder, but not lighter, and certainly not as responsive. 2-10" speakers with 40 watts gives you a Vibrolux Reverb, a very nice amp (and more expensive) but significantly different than a Super Reverb. The most versatility would be putting the Super Reverb head in a Bandmaster Reverb head cabinet, and then have two custom open-backed 2-10 enclosures, and using only one for smaller gigs. That is at least $700 in cabinets, if you want a vintage look, assuming your speakers are good. If you can build your own you could maybe save some money if your time isn't worth a lot.
I think your friend really needs a different amp. How loud does he need to play?