Ahhhh yes.
I have a T3 action in a manners T4 stock and bought the CDI bottom metal. The fit was less than drop-in to say the least but it is do-able.
I think the contour will be right for the factory plastic stock but you will almost for sure have to dremel the inside of the mag well on the stock to allow room for the CDI. You may also have to inlet for depth.
As for AI mags fitting the T3 action ... They are not compatible straight away. There are two options; 1) inlet your action to make the opening for the mag slightly wider or 2) take a file and file down the sides of the feed lips to make it fit.
I've posted pics somewhere on here with my finished product. My rifle now functions flawlessly and looms pretty sharp too.
So, like I said, it is do-able but it will take some work.