Hi Brett, and welcome - from the old country
It's great to hear that you've switched to the K-mount with that rather wonderful K-1II - a truly amazing camera from everything I've read. I look forward to reading your thoughts and experiences.
Regarding the Tamron 28-75 f/2.8, it's a great little lens, offering a faster constant aperture than your D FA 28-105... However, do bear in mind that it's a film-era design. As such, you need to stop it down a little for best performance (though the two copies I own for different system mounts are perfectly usable at f/2.8 - just not "tack sharp"). Also, it's not unusual for these earlier Tamron AF lenses to require some AF fine adjustment - more so than Pentax's own modern glass. But, properly set up, I'm sure you'd like it. On Pentax APS-C cameras, it's my go-to lens, and on my Sony full-frame gear it does a great job when I don't want to carry my much-heavier Sony Zeiss 24-70 f/2.8.
Looking forward to your involvement here