Not too familiar with the K lenses. Just use the Pentax SMC 50mm f1,8, (given), the Rikenon 50mm f2 and the enjoyable Tokina 80-200 f4,5 (i know it's quite dark).

On the market, amasingly, the K lenses aren't that cheap, so I also use Tamron adaptall lenses on my K1000 or the Ricoh KR10x.

However, although, I am not an expert, I have often heard bad reviews about the Takumars designed for the K lenses. It might not be the case for every single lens of that serie, but before purchasing one, make a deeper research regarding that one.