Sometimes a K3 recentered lens mount ring is on ebay look for it, its there I have seen it and it was not expensive.
Speaking of the K3, its an amazing camera and I love it. I agree with Bill, its a 16mm camera you could take ANYWHERE!
A few weeks ago I took the strap that came with the case and attached the strap to the camera which you can do, and you can wear the camera like a saddlebag. I rode my bike with it on streets of NYC and it was fine, I had a Peleng 8mm lens attached to the camera, with 50D Kodak film loaded. Lemme say this, the camera gets really great images, sharp. I now know where to send my exposed film to get it looking its best. Anyway if your gonna ride around with the camera I recommend using a lighter prime lens, I say this because I get hypo while riding and worry the camera is gonna fall by some accident(paranoia) in which case I could always deal with losing a prime m42 mount lens but I VALUE the russian meteor zoom lens SO MUCH because I feel the images it can capture are sharp! I only the lens for tripod or careful shooting, ( my fun run & gun, biking and adventuring lens is my peleng fisheye 8mm which is jus attach t a wide angle lens on the k3, you could do the same but better if you have a large collection of m42 lenses! With the K3 you can do fun, adventurous shooting, the camera body is ULTRA sturdy, I have seen it advertised as being built like some great russian tank which exact name escapes me at the moment. Overall a durable camera that can get really sharp images. I never use the light-meter that comes with the camera, I just use a sekonic light meter (with my lumisphere up!) so far I have been happy with my results and I DONT even have my loop informers removed, no super 16mm or ultra 16mm, no cool laser brighten, although I am saving for it, laserbrighten is a mod to get for the camera for sure! I am still kinda of unsure about super 16mm or ultra 16mm thats kinda of on you to investigate and weigh out the pros and cons. LOOP INFORMERS! GET THESE REMOVED! if you want I can link to some of my footage i shot with the K3 and boy, I am happy with exposures but the scratches the loop informers create bother me,(although most of the people that I have shown my footage to enjoy it, in fact one person told me not to remove the peaky informers but i am, because they dont do their jobs which is to guide the film, I always have to play around with it , but I love it ( btw, this is the camera I learned how to shoot 16mm with so, there is that sentimental thing happening I guess..its also a fine piece of soviet craftsman ship, kudos to Zenit!
The cranking. I dont mind it so much and its a good wrist work out lol. there are tobin crystal sync motors but these are ULTRA RARE and probably command ridiculously prices( you can get like 3-4 k3's for the price of 1 tobin motor, so thats silly, also with the motor you lose the awesome ability to do single frame shooting, aka stop motion or time lapse.
there is a company in nyc that sells a timelapse thing for the camera its called NCS if you type krasnogorsk 3 on google you should come across this cool company. its a bit pricey but a very cool, professional tool, here is the link. I have been wanting this for a while but cannot afford it. I have a scoopic ms and unsure which to get it for but i think I would get it for the k3, this is a topic for another post perhaps.
oh lastly, I came across the lomo developing tanks and I would say get one! so you can save money and and DEVOLP your OWN film, how cool is that? I have yet to do it but again I want to lol - be sure to get the 30m/100ft ones!
p.s will that is so awesome that your viewfinder was widen so you can get the super 16mm frame. Could you post what it looks it I am intrigued!