tube monoblocks and preamp recommendations

There's not only Horn Mono. There are more powerful amps there.
Their line preamp is $995 and pair of their Mono 120 is $3995. 
If you need full function preamp, you can get used Audible Illusions Mod 3A used with phonostage.
'Quickies' can also be successfully driven by either passive preamp or solid state. Solid state preamp technically should give better transparency and lower noise floor. 

The Altec is a high efficient type speaker so I don't think you will need globs of power. You should give Mike a call at QS and see what he recommends. BTW, years ago I used the Mid Mono's ( 50 watt) with low efficient Spendor's and they worked just fine!

If you finally want yo see what a Single Ended preamp sounds like without breaking the bank ,and Remote controlled options and a choice of 2 different 
DIRECT  Heated Triode https://simplepleasuretubeamps.wordpress.com/ preamplifiers. I bought a deluxe all Lundahl transformer based model .
This I can guarantee nothing but yhe best parts used money can buy to complement the superior craftsmanship. Check it out p..sent
If uou wanted to see my preamp and build let me know I will send you a few pictures. If this were CJ made or AR it would be 4X that without question.

I have a pair of diy model 19's, with gpa 416 drivers and crossovers, 811 horns and vintage 802g drivers.
I have had everything on them w5m mono blocks , st70 dynamo and ss macintosh, it all sounds fantastic with a pair of 19's.
I don't know if they can sound bad with any decent amp driving them.
They really need very little power to put out massive amounts of good sound.