Production numbers for "Sprint" are deceiving because they include both Firebird AND Tempest vehicles.
I remember calling an Engineer at Pontiac back in the mid-eighties and he told me that for the 1968 Pontiac Firebird Sprint w/Manual (or "M") transmissions, 3,514 were made. According to the chart, that would mean a little over 2,000 Tempest Sprints were produced.
5,609 Total "M" Sprints (-) 3,514 Firebirds = 2,095 Tempests
Hope this helps!
I can tell you that for a 6 cylinder motor, they are EXTREMELY QUICK off the line and in top form can easily waste many corvettes or any other V8 of that era. They can be temperamental motors however and require some babying. They love high RPM and because they are belt-driven (not chain) are known for their smoothness. They really don't get enough credit. They represent the beginning of the Overhead Cam engine. The PMD (Pontiac Motor Division) embossing on the cam cover represents a truly innovative group of engineers way ahead of their time!