Dahlquist DQ10: what is best way to power?

I think the Apt Holman's are to old to fix and darn near anything you buy today will outclass them.

I bet something like an Outlaw Audio rr2150 would sound pretty good for around $500 used.

How much do you have to spend?

I've sat in front of several DQ-10's. The best I've ever heard them was near 30 years ago with a Audio Research SP10 & Kenwood LO7M mono blocks. When you say restored in every way, I assume the piezo has been disassembled and the diaphragm damped.
I would suspect 100 watts or higher that is an good dynamic sounding amp would do a good job here, 200 would be better. I've never heard them with a tubed amp, I haven't seen phase angles on these speakers, but I would assume an 80 watt or so plus tubed amp would do a good job with these, if I recall correctly, they run 5 to 8 ohms at 86db sensitivity...
I'm sure when you give a budget, you will get several good recommendations

There is a Fort'e model 3 for sale for $400 on this site.When I had the DQ10 that is the amp I used with great results. It has 200 watts and will drive them real nice!

Without knowing the budget, here's a few. A vintage belles, or hafler would be nice. Nakamichi PA7 would be high on my list. If I had them, I think a belles 400 would be my first choice. I think it would be cool to pair them with something from roughly the same period. Threshold would be another great choice.

In their day, they sounded great with a Bedini Class A amp. The more power the better. For class A/B I would look for 200 wpc.