+4/+6

take the extension length, times 2, add that to the stock length and that will be how much you need
 
Just put on a +4 myself... originally had a 104 link chain... this was one link too short, ended up getting really long chain and cutting down (forum member oregondunes hook-up, thanks)... this is what would recommend. might also depend on sprocket sizes.
 
I would think so. I have 130's in stock. they just about work for every extended swinger made.

I run BIG sprockets on most of my bikes. Biggest I can up front and what ever is necessary in the rear to make my ratio right.

if you want to learn more why, just ask.