There's a lot of info in the Adaptall Club sub-forum and in the Tamron Adaptall lens review section.
https://www.pentaxforums.com/forums/122-lens-clubs/59769-adaptall-mount-club-...ml#post3346937 Tamron Adaptall Lenses - Pentax Lens Review Database
(note separate section for the SP lenses)
And on the Adaptall.org site mentioned above. (Do read the history articles too.)
adaptall-2.org
And do search for 'Adaptall' in the Articles forum
The Adaptalls are generally of high quality, both optically and in build quality, with development and expense going into the optics while taking advantage of the competitive economic advantage of using adapters rather than unique barrel mounts. Most of the SP lenses of the late '70's and early '80's are optically comparable to all but the very top line lenses of that era from OEMs.
Many of the second tier, non-SP lenses of that era are also very good optically differing from the SP line in that they incorporated industrial plastics in the barrel and usually were limited to F/3.5 - 4.0 apertures. This was an era of intense exploration of computer aided design for both optic formulas and mechanics with SP lenses building on what was learned in the less expensive non-SP development and marketing process. Many of those lenses are the precursors of the modern Tamron SP AF lenses. Unfortunately, that was also the period when OEMs began to develop electronic AF and AE mounts which couldn't be economically replicated with adapters and the Adaptall concept was abandoned.
Today there are fine bargains in Adaptall SP lenses for those willing to forgo the pleasure of complaining about Pentax auto-focus problems and the nominal advantages of Di coatings. Fortunately the PK mount adapts well to the Adaptall concept.
Take the SP 80-200/2.8 (63B) as an example. Typically 1/3 the cost of the SP AF 70-200/2.8 and I'm unable to tell the difference between the two lenses without a helpful nudge from EXIF after normal tweaking in post-processing.
The SP 300/2.8 (60 and 360) lenses are quite capable when used for nature or tele-close-up tasks at about 1/2 the cost of equivalent AF lenses.
The SP 90/2.5 - 2.8 (52B/BB) lenses and the excellent SP 180/2.5 (30A) macro lenses continue to be well respected for their intended purposes even today.
The SP 35-80/2.8-3.8 CF Macro (01A) is a favorite general purpose lens with a good rep.
Both the 350 and 500mm mirror lenses are still considered among the bet of that type.
Optically I cannot tell any difference between my 1.4x TC (140F) and the more modern Tamron Pz-AF 1.4 converter. Both play very well with most newer lenses as well as the Adaptalls and have good reps.
I've owned and used each of these lenses along side their modern AF off-spring and find very little advantage in the newer lenses except for occasionally being thankful for AF owing to 70+ year old eyesight.
When used on-task for static macro and telephoto tasks manual mode and the inexpensive PK adapters combined with instant review/histograms leave no points on the table relative to the more expensive PK/A adapters.
May I suggest starting with three items that shouldn't cost more than a good steak dinner -- the AD-2 28-70/3.5-4.5 CF Macro (44A) and/or the 35-135/3.5-4.5 (40A) lenses with a PK adapter (the known good PK/A adapters cost about $80 today but can sometimes be found for less.
My all time favorite -- the SP 180/2.5 Macro -- but I'd have to vote the SP 80-200/2.8 the most useful Adaptall of all and it has comparable IQ when used side-by-side with the 180 in the field.
If your skill set includes manual focus and exposure try 'em. You'll like 'em.