Another Koni-Omega shooter here, they're great cameras if you can get on with them. I tend to use mine more in the winter because they're easy to operate without taking off my gloves.
Some considerations about the 135mm which you may or may not be aware of:
In general, many of the Konica-made Koni-Omega bodies don't have the framelines for the 135mm, nor is there a 135mm scale on the focus wheel. My Rapid-M doesn't have either. The later Mamiya-made Rapid 100 and Rapid 200 bodies do have them. The earlier KO's could be fitted with the 135mm framelines from what I understand, but I've never seen one.
The close focus distance limit for the 135mm is around nine feet, so you won't be able to get a tight headshot. The 180mm's closest focus distance is about 12 feet.
That being said, I'm sure it's a great lens. I have the 60mm, 90mm, and 180mm and they're all good. The 180mm I only bought because I found a really good deal. I use it more than I expected I would.