delbiker1 

As stated in a previous post, I am using 9 speed, Ultegra 6500 short cage derailleur with 6400 bar end lever and either 11 or 12 speed cassettes. All I do is change the cassette and the chain, using the same for both. My front is a 6750 crank set with just 46-32 rings. Shifting is excellent, once you get use to the travel of the lever to make the shift. I also have a 1 X set up on a bike, front is 44 tooth, rear is a 12 speed shimano 11-34. I can easily switch to a 42 front with 11-36 rear is I need a wider range. You cannot make these kind of changes as easily and at as a low a cost with indexed shifting. I have 3 other bikes that all have indexed brifters. I like both, both have a place in my bike line up.
You may or may not have to do some minor adjustment with the limit screws to get the dr to reach all 12 gears, real easy. As long as I have my Poprad, it is going to be friction shifting, whether a 1X or 2X.

RH Clark

I've set up several odd ball systems using friction shifters.. Hold your derailleur as if it had a chain and if you can adjust it so the cogs line up with your lowest and highest gear it will likely work. The only other factors are the cable pull distance of the shift lever and the chain length. I've never had a downtube friction lever that wouldn't pull enough cable, but I have had to fool with chain length sometimes.

I absolutely love the simplicity of friction shifting. Just line up the derailleur wheel cogs with the cassette high and low cogs by adjusting the high and low limit screws and your shifters are tuned. There is no tweaking barrel screw adjustments and listening for out of sync noise. You likely won't have to adjust shifting now for years.

ArgoMan

WOW! So, I went home last night and watched the Park Tools video on indexing the shifters. Got it all set up where it is operating really smoothly in all cogs, except for the smallest, which makes a bit of noise. No biggy, as I never use it and I think the cassette may be just a tiny narrow at that point. But today I flipped the switch to friction shifting, and MAN! I am now a friction shifting disciple! I can't believe how cleanly it shifts and how much fun it is dialing in the right gear while flying down the road! I find it no more difficult than operating the system in index mode. It's so cool how you can give the lever very slight adjustment to dial everything in. Thank you for everyone's guidance!