Wow, that is one hell of a good friend!
YBA-1's are excellent amps that sound fantastic and were very solid amps. They have high quality Hammond Transformers in them, not the crap you find in amps today. People used to buy these as a lower cost but every bit as good option to Marshalls back in the day. They have come up in cost some due to the cat being out of the bag but are still very reasonable by comparision. Those will be made better than any modern Marshall. Maybe you can cut a deal with a trustworthy tech to restore one for you for the the other......if it even needs anything. I would just replace those filter caps and let it rip. I doubt it needs any more than that. Whatever you do don't give away any of that vintage glass. They probably have high dollar Mullards in them. GREAT SCORE!!!
This is what you should expect to get straight in and cranked:
http://www.youtube.com/watch?v=juTBJ4ATtfw