Suntour cyclone M2 rear indexing?

I recently bought a 1984 raleigh competion frame/forks, which came with the original suntour cyclone M2 mechs. I thought i'd have a stab at setting it up with a 7 speed shimano (NOS dura ace 7400) freewheel with 105 index shifters, took a while to set it up on the bike trainer (no cable adjuster on the rear mech!) but i got it working perfect - then i rode it and it started missing gears, so i switched it to friction and that works ok.
I used new KMC 9 speed chain (which does change cogs beautifully front & rear). I'm using a shimano 600 chainset.

Originally the M2 rear was 6 speed friction AFAIK.

I'm looking to buy a suntour 7 speed sprocket and (braze-on) index shifters, but the 80's suntour shifters i see for sale on ebay are for other types of suntour gears (i.e. Not cyclone), would these be fully compatible?

Am i better off just sticking with 6 speed for indexing, or do i just forget indexing and stay with the 7 speed shimano/suntour hybrid setup in friction mode?

Also is there a way of adding a cable adjuster to the rear mech?

Velobase indicates that the M2 cyclone was designed as a friction shifting system so setting it up friction may be the best for shifting efficiency. Maybe some power shifters?

I know that Shimano 600 was indexed in the early 80's as I have a very nice example of that in my parts box, but Suntour lagged a bit behind them and the early suntour indexing had a poor reputation (although I've heard some say its because manufacturers didn't spec the correct chains often).

Percybigun":31wqpa02 said:

(no cable adjuster on the rear mech!) but i got it working perfect - then i rode it and it started missing gears,

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I reckon you stretched the cable a bit and/or it all bedded in and voila it started missing gears. Get one of those inline barrel adjuster things and put it somewhere close to the bars so you can keep things taught. They are a cheap experiment.

Either that or sell me the rear mech

I’ve sorted this problem, it was because I had cut the chain 1 link too short. Now it’s the right length, the indexing works fine on everything on all the gears, despite it being a mucky mixture and the rear mech supposedly 6 speed friction only!

Re:

Also moving the back wheel further forward in the rear dropouts, helped to cure the problem