Jim -Why not give us a specific example of an amp you are trying to recap? I'm sure we can give you a better idea of possible part selections.
Remember that most electrolytics are -30%/+70% at best. There is really no difference between a 40uf and 47uf cap. Also voltage ratings are minimum - it's fine to go higher.
If you find yourself recapping vintage gear often, consider getting one of the older cap checkers. My favorite is the Heathkit IT-11/IT-28, but the Eico 950B or Sprague's are also very nice. They let you measure leakage at up to 600vdc - and are perfect for reforming older electrolytic types.
- Gary