As one who has had a 1979 R100RT in my garage from new, I agree that they are rather old fashioned.
That doesn't mean they are without charm, far from it, & they are still a very capable motorcycle, but you will find them very, very different from an oil-head boxer.
There is a surprising difference between a 100/7 & the last of the line R100R. Models with 40mm carbs & 32mm carbs, 40mm exhausts & 38mm exhausts, different compression ratios; different forks, instruments, switchgear, it all adds up.
Every year there were numerous changes, some small, some much more significant, so the later models generally have a lighter feel to the controls.
You could do worse than study this book, by Ian Falloon
http://www.veloce.co.uk/shop/products/p ... otorcycles & Scooters&
I ride a 1200RT at work, & have a GSA & 1200RT at home, so my old girl doesn't go far nowadays ( although I did a 1,200 mile trip around Scotland last year with an air-head riding mate, & I loved it) & when I get her out, I really don't enjoy the first 20 minutes or so.
Controls a bit heavy, acceleration & handling fine, brakes ( even with the 1984 onwards Brembos retro-fitted ) a real eye opener.
Then after a while I think "Actually, I've done so many miles on this old girl" and I start to enjoy it………
Would you take to it ? I don't know, but I'd suggest if you do try one, don't just ride around the block. It takes a while to like.
Remember your first glass of beer ? To be honest, most of us didn't enjoy it, but your older mates drank it, so you tried it.
After a while you got the taste for it perhaps ?? That's what it's like.
Good luck with your decision.