You won't be able to use an additional field with the out of stock indicator. After all, if the radio field was for "green" or "blue", and you have 1000 blue, and no green ones left, would the attribute grid box show up, or show a X? In this senario, you are looking for an AJAX dynamic type of attriubte, with stock look up capabilities, which isn't available as yet with Zen Cart.

As for the stock question and file permissions, the coding doesn't use affect the stock levels, as this is still handled via the standard Zen stock control coding, or the Stock by Attribute module.

Finally - mcshane78 - have you installed this module? Did you follow the instructions which are included with the module, and "fairly fool-proof"?

Absolute