I'll take a stab at this.
Now this is my opinion of why nobody has/would build a 326 powered Stocker.
(1) The 326HO carb is a an AFB. It seems that most all the popular Pontiac combos are Q-jet equipped. It has been proven that legal 750 Q-jets will feed even low 9 sec SS engines, & 10 sec Stocker engines. Therefore, a Q-jet would not be a choke point for a 326 engine.
(2) The NHRA hp factor of 285 is just too high to make the 326HO competitive. There are later Q-jet equipped 400 cube engines that have a lower hp factor. The '68 Q-jet equipped 350HO has an hp factor of only 305. That would make it much more competitive than a 326 @ 285hp. Don't know how low the 326 engine hp factor would have to be in order for it to be competitive. But obviously, if you get the hp factor low enuff, you can make most any combo competitive. There have several very competitive 4-cyl cars.
http://www.classracerinfo.com/Engine...0&MAKE=Pontiac
(3) There are no legal replacement 326 pistons listed. So, anyone who wanted to build a 326 Stocker would have to get a piston made & NHRA approved. Adam Strang did this for the '68 Pontiac 350.
(4) Not sure, but I assume that the auto trans equipped 326 cars came with the 2-speed. I think you can now run a 3-speed. But, this was probably a major consideration, back when you had to run what it came with. I'm quite sure that's why there were VERY few '64-'66 GTO Stockers which ran an auto trans.
(5) Bottom line is that there are just too many other Pontiac combos that are much better choices, for a variety of reasons. Therefore, I don't expect there will ever be a 326 Stocker built.
"...People build the 305 ci SBC 3.736" bore and run well."
As to that statement: The '80 Bird I bought in recent years had a Q-jet equipped 305 in it. So, just out of curiosity, I just looked up the 305 powered '80 Pontiacs.
For all Pontiac models except the Birds, the hp factor is 235. That's 50 hp LESS than the 326 Pontiac engine, plus it has a Q-jet. Hey, at 235hp, the 326 MIGHT be competitive. Don't know.
http://www.classracerinfo.com/Engine...5&MAKE=Pontiac