Help me identify an amp

Man, this should be in the HI-FI hall of fame.  I would love to hear what it can do after you get it in working order.

8417 are out of production and unavailable. Quicksilver used to offer an EL34 mod for their 8417 monos.

Good testing 8417's are still available for $400-$500/quad, though I would advise picking up spares/matched quads in a timely manner as they are considerably more rare than good vintage EL34's (which also run around $400-$500+/quad).

DeKay

Looks like an old Dynaco ST-70K kit.

Here’s a thread that contains photos of the original documentation. They would be worth downloading and saving should the amp need service:

https://www.diyaudio.com/community/threads/st-70-gsi-mod.324845/

It is probably in good working condition, but as others have said, it should be powered up slowly with a variac over a couple of days to allow the electrolytic capacitors to reform. If you’re not comfortable with this, you can probably find a local tech or even an experienced tube hobbyist who could do this and generally check the amp out. For further, more technical advice, Audiokarma is a good place to post that will allow you to communication more easily with someone who might be able to offer help.