help with pentax adapter!

Hi nex crew,
i just inherited a mint 50mm pentax smc takumar f1.4 lens
(off my dads old pentax asahi spotomatic 35 mm film camera)
i want to get an adapter off ebay but im not sure which to get?
Do i get the pentax k, the pentax pk or the pentax m42 adapter?

If anyone has used the old 50mm smc what adpter did you buy?

cheers
SB