Eaton belt approximation. Opinions?

[wjfawb0]

Hey all. I am installing my new aluminum built block into my 03 Cobra this weekend hopefully. I wanted to run this belt size idea by a few of you all and see what you think.

I have been running a K080745 gates belt on my car for over 20,000 miles with no problems. Here's the old setup with that belt:

2.80" upper
100mm auxiliary idler
2x100mm idlers
1x92mm idler
stock lower
stock alternator

Now I upgraded to a PA130 amp alternator and installed a metco 3.2" alternator pulley. Here's my idea about belt length change with the new alternator pulley:

 

[wjfawb0]

Am I crazy, or does that sound right? I have so many belts laying around from previous pulley combos, I think I'll just try them when I get the car together. If I have to, I'll remove th eauxiliary idler to get one of the to work until I get the right size. I have to break in the motor and clutch anyway.