What size slicks for stock rim?
 

I am looking to buy a set of slicks for FD, what size will fit on a stock FD rim?

I don't think you'll find a set of true slicks. ET streets are about the closest thing you can get. 26-10.5-16.

I've used them on a drag Nova with very good success. I've never used a set on an FD however. I've heard Ryan has had great success with them on his FD.

Will 23.5x10.5x16 fit?

The 23.5 will have less of a sidewall and probably not much of one. That is how tall it is, 10.5 is the width.

the optimum size would be the ET streets in a 26x11.5x16.