Hey all.

I got a great deal on a replacement Ultegra 6500 crankset for my road bike, and I'm taking the old one and putting it on my fg/ss.

It's a 130mm BCD. Is there anything else I need to be aware of? I'm probably going with a 1/8" width just to make it complete, as I'm using a 1/8" cog and chain.

Should I put the chainring where the smaller chainring would go was for a cleaner chainline, or should I connect it directly to the crank-arms where the larger chainring would go?

You should do everything possible to maintain a straight chainline. Use whatever arm you need to to make that happen, or even get a new bb if necessary.

I have a great chainline right now with a 107mm square-taper BB, so I assume that if I use the 109.5mm Octalink BB and the inner-chainring position, it should be just as close, no?

With a 6500 crank and 109.5mm octalink BB, put the ring on the inside and you should have a 41mm chainline, which will not be perfect but probably no more than 1.5-3 mm off, depending on your hub and cog. You could actually install a $2 spacer with your BB which would give you the correct chainline.

See here..
https://www.sheldonbrown.com/bbsize.html

and here...
https://www.sheldonbrown.com/chainline.html

and here (for 1mm BB/freewheel/cog spacer)...
https://www.ebikestop.com/freewheel_s...each-18668.php
This thing is described as a freewheel shim but you can also use it to move your BB/crankarm/chainring to the right one mm. I've tried it and it works, but use a bit of blue locktite if you use a spacer.