John - I'm partial to the MSHP's, but here's a few things to consider.
It's fun to return these back to in-service condition but depending upon the choice of cars it may be much more cost effective to buy a turnkey one, or in other words an SSP that has already been returned to in-service condition. From that perspective I would let my goals (something to enjoy right away or to restore over time) and my budget steer me in the appropriate direction. Personally I won't go through process of having a car stripped to bare metal and repainted again as it can add quite a bit of time to the process and it costs too much compared with the car's value. In the case of my MSHP it was an easy decision given why I bought it to begin with; I am keeping the car barring anything unexpected; the black & white paint and other paint layers needed to come off in order to end up with something I would be happy with long term. From a documentation standpoint an MSHP one would be easier to return to in-service condition due to all the research and documenting that Eric (Mustang Retriever) has done.
A turnkey 93 MSHP is available (or was at least recently) that is basically a twin to mine (white with ruby red interior). It was the last in-service MSHP Mustang so it has an interesting history. The last Trooper assigned to it is a Sgt. with the MSHP. Also a few that are not returned to in-service condition have been listed for sale recently some of which may still be available. Try a few different searches in the SSP forums (such as Missouri or MSHP) and you should find some recent adds and contact info for sellers.
Don't know that I've seen any pictures of a completely finished Kansas SSP, but John Malloy (his username on this site is xxtrpr) was working on one that he had listed for sale several months back. You'll have to send him a private message to see if he still has it or not. Use the search function on the SSP sites and I think you'll find some info on his car. He also has some photos (none appear recent) on his Fotki site
http://public.fotki.com/xxtrpr/
The only other Kansas SSP I can recall someone talking about on one of the SSP forums was a Roller that if memory serves me correct the forum member had a friend trying to sell the Roller. A Kansas SSP would be rare and certainly not as many photos; documentation; etc. available on them. That's not to say you couldn't do as I did on my North Carolina State Highway Patrol SSP and find some great contacts who help you to document how they were correctly equipped at the time. I'm been fortunate with that and am wrapping up a Restoration Guidebook on them.
These are just some of my thoughts and not really intended to answer, but provide some things to consider as you make a decision that suits you best. I'm sure others have insight they can share as well. It's a great niche of the Mustang hobby no doubt. Good luck in your quest.