Only the Takumar Spotmatic-era lenses will need an adapter. The rest will mount straight on. There's a
which shows exactly how to meter with the older lenses.
If I were you, I would spend the money necessary to get one of the genuine Pentax-branded adapters or a reasonable facsimile from the same era. It will be more expensive, but better in the long run. I think there are still a couple for sale in the forum marketplace right now; I can PM you the seller's name if you're having trouble finding them. Look for people selling M42 gear. The adapter is the same regardless of which Pentax bayonet-mount camera you are using - they introduced them almost as soon as they went from screw to bayonet mount back in the 70's and went on making them for some time (even after they dropped "Asahi" from the brand name), and provided the adapter itself is reliable, it makes no difference which camera you use it on.
If you're going to go aftermarket, make sure that you go for an adapter that is advertised as guaranteeing infinity focus. The adapters that need a special tool to get them off can be a problem; the older, "official" K mount adapters can have their retaining spring pulled in with a fingernail and easily rotated off.
If you are in any doubt, try it out on your MX before mounting it on the DSLR - because the MX's mount structure doesn't have electrical contacts, there isn't anywhere near as much chance of doing damage if you find yourself struggling to take the adapter off. When you're comfortable with what you're doing, then try it on the DSLR.
The older Pentax K-mount camera manuals advocated threading the adapter onto the lens first and then mounting it as if it were a bayonet-mount lens. Make sure before you do this that you are able to get the adapter on and off your DSLR with ease.
Good luck.