Hi Jerry,
You can get by with an AM generator for antique radio work. You have to decide whether you want a vintage S.G. or a modern one. You can buy a new S.G. from Antique Electronic Supply for around $160.00 (I think) that will do everything you need and will be accurate since it is new.
If you want to buy a vintage S.G., make sure it has an R.F. frequency range of at least 100 kHz to 20 mc to cover AM and SW bands and use for FM alignment. Most will cover up to 60 mc. You'll also want an audio signal option (usually 400 cps) for trouble shooting radio stages from the 2nd detector output to the speaker.
The downside of a vintage S.G. is it may need repair and probably won't be accurate. Repair is usually just a matter of re-capping and most are easy to calibrate if you have instructions. Or, you can just check them with a frequency counter or beat them against known frequencies. Just about any service grade S.G. is adequate for antique radio work. I have a very simple NRI Model 88 that I bought for $2.00 at a swap meet and then re-capped and calibrated, it does everything I need. I also have an HP 606A that is deadly accurate but takes up a huge chunk of my bench.
(Good hand warmer in the winter though)
S.G.s are readily available at swap meets, surplus electronics sites on the Web (A.G. Tannenbaum and W.J. Ford are 2 good ones) or on ebay. Don't get caught in a bidding war, as soon as one mint Hickok 288x gets sold, another one comes along.
Hope this helps.