It partly depends on the year, but replacing the signal chain capacitors should be unnecessary unless any test bad. Old "paper in oil" caps are the oldest and seem most prone to failure. Dry film caps might last several lifetimes so replacing them arbitrarily isn't practical. IMHE whenever a novice starts fixing things that aren't broken it invites more trouble than improvement. JM2C on that.
Electrolytic caps DO suffer degradation with age so it makes sense to replace them in an amp that age as a matter of maintenance. This would be the power supply capacitors and any preamp tube cathode bypass capacitors. In a two power tube amp there are sometimes a couple more electrolytics used for a bias supply. You're amp probably won't have a bias supply.
If your amp uses a multi section can type capacitor for the power supply I've had good luck with JJ capacitors. I like the value options they offer and I've used them a few times with good results. Admittedly, I haven't tried any others because I haven't had to. If your amp uses individual axial lead capacitors F&T are popular, but I can't speak from experience since I stopped using axials when the brand I was using stopped working for me.
With an older amp like that you may have a two prong AC cord. For safety reasons this should be changed to a proper three prong grounded cord. I'm not being a fuddy duddy! You're holding a metal mic in your hand connected to the amp. A lack of safety ground in this case is not cool, it's just careless and more than a little dangerous. Especially if you play dives where God knows who has serviced the electrical.
Many of the older single ended (one power tube) amps make wonderful harp amps. The best thing you can do to make it a reality is service it properly. Clean all the jacks, switches, pots and tube pin sockets. Replace the electrolytic caps. Retrofit an AC cord with a proper ground.