Drive idler pulley and drive tensioner pulley idea. Doable?

[Swift+]

New here.

I've read the topics on here regarding the pulleys and have an idea towards installing aluminum pulleys on these cars.

Drive Belt Tenstioner Pulley; 76mm x 17mm Flat Steel, 31mm wide
Drive Belt Idler Pulley; 109mm x 17mm

Not sure if the outer diameter specifications above are correct; are they? (Just double checking)

Since the idler pulley and the tensioner pulley don't affect the ratio because they are on the outside of the belt; in theory, getting 2 aluminum pulleys with a combined diameter should work. example: 76mm+109mm=185mm Instead of 76mm tensioner and 109mm idler; I might be able to install a slightly smaller idler pulley and bigger or same size tensioner pulley based of how far the tensioner pulley tensions and how far away the belt is from touching the casing on the idler pulley side. See pic below.


Bigger: https://drive.google.com/file/d/0B9h...it?usp=sharing

I will take any input you guys can give me. Is it doable?