If it's an 8 ohm or 4 ohm speaker you should be fine for test purposes. I'd suggest rebiasing when you do it though just to be safe. If you n
The amp is "rated" at 85 watts - but even cranked up you won't get more than about 35 watts or so out of two tubes. Vintage amp wattage ratings are almost always exaggerated...based on max power dissipation, which you can get - if you want to have your tubes last for 30 seconds or so.
If it's a vintage speaker chances are it wouldn't handle 45 watts without a recone anyway.