Can 5881 Take High Plate and Screen Voltage?

Watched an interview with Mike Soldano where he said to put 5881s in his SLO100 amp.
This amp has about 500V on the plates and the screen is not too far behind. I have several
1960s production Tung-Sol 5881s and while the bulb is small the plates look
huge. I know that they are a good tube but am wondering if they are designed with
huge margin on the specs. Mine are not JAN military but I've seen them and they look
the same. This guy states that Mil 5881s can be pushed far past their specs - but it is the
Internet so who knows:
What is your favorite 6L6/5881 power tubes for a Soldano SLO? | The Gear Page

Some people state that Sovtek 5881s are stock OEM from Soldano:
What is your favorite 6L6/5881 power tubes for a Soldano SLO? | The Gear Page

I'm wondering if current production 5881s are just built the same as 6L6GC s?

If buying new tubes for such an application it seems to me that the Tung-Sol 7581A is
probably best since it is rated for the high voltages and the price is not bad at all. I'd
probably put these in my son's Fender that has the plates just over 500V.
 
I just bought a set of new Tung-Sol 7581As for my Music Man 75, which runs 700v on the plates, but has a different bias setup than most amps. I'm gonna see how they work out. I've been running a set of JAN Philips 6L6WGB/5881s in it for years and they still test new...

A couple of things you might want to think about, though: One is that there's a difference between the 7581 and the 7581A. Make sure you're getting the A... The other is that the 7581A is a 35W tube and the 6L6GC is rated at 30W, so there will be more headroom, which means the amp will be about 15% louder before it starts to give that nice output tube breakup that we all love... I use my MM for bass, so that's a good thing for me, but it might not be what your son is looking for.