It's a donated pulley (aluminum billet, cnc) from the guy who sold me the blower on ebay.
It's one he had left over from some twin Vortech kits he made for Vipers.
The original (two) V-belt pulleys are nested inside; same bolt pattern and same depth.
I lucked out...
He suggested my going to a junkyard and taking the entire accessory drive system off a '90s Dakota and using 1 belt for everything. He know what he was talking about...
I'd think that would be an easier way to go about it.
