Will Push-Pull Triode amp 20-25 WPC work?

I would say yes, it would work. Your speakers are not very efficient, but you have a small room and you listen at quiet to moderate levels, so it should work. 1 watt will put you at 87 dB 1 meter from your speakers, which is certainly moderate SPL in my opinion, especially in a small room. So 22-25 watts should be plenty.

I've been considering the same question, but my speakers and room size are different. My room is 25 X 15 and my speakers are 91 dB, 8 ohm. I'm considering playing with a 300B tube amp, and believe that 20-25 wpc would work in my room too. My room is larger, but my speakers are more efficient. I'm currently using a 100 wpc amp that has PLENTY of headroom.

Thanks for your response. Maybe I can help you with your question: I too have a large room in the basement, similar to yours, and have Tyler Decade D10s, 91 db sensitivity and 8 ohms, and are driven to any sound level I wish with 30 WPC Class A Thor MPA amps. So go ahead:) Maybe so will I.

I have driven 89db, I think sensitive Acoustic Zen Adagios with a 22 watt 845 SET and it worked OK. I don't think it gives your amp choice gives you much headroom, but tube amps clip in a benign way of course.
I think the advice, as always, would be to try before you buy.

It would bve great to try - these days with everything bought on line and the paucity of dealers, how does one try?

At up to moderate levels, I agree with those above who advise that it should work. I use a 25W/Ch. 300b amplifier with 91db speakers in a larger room. Your Allison 4 speakers have a very benign impedance.

FYI:
http://stereonomono.blogspot.com/2012/06/allison-four.html