Easy.
Bar end shifters depending on the ones you buy may be both. Index and friction. All newer ones are. Older ones may only be friction.
If you like STI them by all means buy STI. Only problem is you may only find 9s systems. This means new hub if you have an lder 6/7 speed rear hub. Ig you have an 8s hub then all you need to do is buy a new 9s cassette and a new chain so it all is new and works fine.
As far as the rear spacing. You a re right. Basicly you can spread yourself. Many do this including me on old frames. No big deal. This however may take some muscle power in your part.
Voila! You have a bike with new 9s system and STI as you want.
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Xavier Cintron - www.bullteksports.com