With my double roller, the reluctor would have made contact with the chain links. I had to space the reluctor out about 1/8" or .125", or the thickness of the reluctor itself. I simply cut the center out of another reluctor, so it would still be keyed on the crank. About 2.5" over all diameter. I installed the "spacer", then the reluctor the crank sensor actually reads. I am still in the process of getting everything together so I have not run it yet, however there appears to be no harm in how the sensor will read.
You can't use a gear drive because of the noise interference with the knock sensor.
If it were me I wouldn't. I would rather run a factory timing chain as opposed to disabling the knock.
Also, I have heard it is not suggested to run a gear drive with a roller camshaft. I have no idea the reasoning behind it, but it could lead back to roller camshafts being more commonly found in EFI applications where a knock sensor is present. Again this is something I'm only heard second hand and have never had experience with. I've never looked any further into it because I personally hate gear drives because most guys simply install them for the "blower" whine.
ya i wouldnt go without the knock either... youd be taking a chance on ruining that vortec 350. i dont know why you want a gear set up inless you want that blown whine... to much work to make a little noise for me lol... go for the real deal!