I had a 326 in my '64 LeMans; it was sometimes referred to as a "baby GTO" in that particular guise - it had the same four barrel as the "lo-po" GTO, true dual exh., and a Muncie 4 speed. Basically, it was a GTO without the badging and fancy woodwork, and a 326 instead of the 389. That thing was a pretty good runner in factory trim, and would hold it's own against almost anything of similar size, and many with bigger engines, as well. If it had the benefit of a good rebuild/blueprint job, and some cam and flow work, it can put out very respectable performance. A set of Super Duty heads or other hi performance factory or aftermarket items, a GTO Tri-Power or other triple-deuce or dual quad manifold, some headers -- well, like I said, the right build, and it might really surprise you. There are several sites on the "net" that are Poncho oriented, and a lot of info out there. Of course, for the same amount of gold, or nearly so, you can build a 400 or 455 and have just that much more oomph. There is virtually no difference in the basic design from the earliest Pontiacs to the latest.