Never found anybody who was able to get one of these things to work PROPERLY on anything other than a K-40 Model 7 radio (the tiny one), however, for what it was, that little rig sounded pretty good on AM.
I myself, used to own a K-40 Model 8 (rare) radio, which was pretty much like an old Uniden PC-66, only the speech processor was actually a BOARD mounted INSIDE of the radio itself. Although it came with the K-40 microphone (magnetic mount that definitely did NOT lend itself well to mobile use), the mic itself did NOT have an internal speech processor like the model 7's mic did.
After the K40 microphone came apart from constant mobile use, I replaced it with an Astatic power mic which worked much better.
Then, after I removed the radio to sell the truck, I noticed that the internal speaker began sounding crappy... as it had begun to dryrot. So, I took the speaker out and installed a 2 pill stinger board in place of the speaker. Rig would DK over 25 watts and swing to over 100. However, it was getting into my neighbor's telephones because I was using a Midland endfed halfwave vertical and no doubt getting lotsa rf in (and out of) the coax. So, I eventually sold it. Wish I hadn't, as finding a K-40 Model 8 in good condition nowadays is like finding hen's teeth.
Good luck with your project. Let us know HOW you make out with it.