Soldano Astroverb Clone Speaker Recommendations

[W5FH]

Hello-
    For readers who have a few moments I am seeking advice on speaker recommendations for an amp I just finished. It is a copy of the Astroverb preamp feeding into a fixed bias Hiwatt phase inverter driving a pair of 5881's. P/I and power section designed to be as clean as possible. Using a slightly oversized Heyboer output transformer (APD-8025H) and NOS USA Tungsol 5881's. Upgraded the reverb driver and added Sluckey Trem-O-Nator for a really nice vibrato.
    The amp is sounding good and guitarist really pleased (pics in amp building section). The upgraded P/I and power section really brings out the tone of Astroverb preamp. It is built on Deluxe Reverb chassis in same 1x12 combo cabinet using a Celestion G12-H-75 speaker. This was the guitarists choice of speaker for a previous build of a clean pedal platform (copy of Fender HRD ML212).
  Question #1. The G12-H-75 is really sounding nice in this combo but wanted to ask other Astroverb users for their preferences. I have been reading various message threads and it seems Astroverb users were noticing the speaker choice was more critical to the tone.
  Question #2. I am getting a Bassman 2x12 closed-back speaker cabinet built as an option to this amp and to test a future build using pair of 6550's. Any speaker recommendations for this? Would only parallel connected speakers be considered, is there ever a reason to series connect two speakers (I am newbie to this).
Thanks all.

[scstill]

Here is a great article I was reading today.
Talks about 212 selections toward the end.
Remember speaker sound is very subjective.

https://www.guitarworld.com/features/how-guitar-amp-speakers-work