Side tracking here but I want to explain something.:yes:
The original GM 1968-72 Nova tachometer was specially designed to fit the engine ordered with the car. There are several tachometers. How do you know which one fits your car? The link below outlines the basic differences between the tachometers. There were some changes made to the tachometers during these years.
"http://www.chevynova.org/NovaTachs.html"
A tachometer system is provided for a motor vehicle having an engine selected from a plurality of engines having unique maximum rated engine rpms.
I may be wrong again here (don't think so, but maybe) but aren't engine internals, bore, stroke, cam, type crank, etc. the main things to be considered when determining an engine "red line". Piston velocities are what I understand to be the main factor. What these guys (like MAKESHIFT4) are talking about is a maximum shift point, not an engine red line. The red line is not the point where the power starts to drop off when shifting; it is the engine speed in rpms, that when exceeded, may result in catastrophic engine failure. In other words, the red line is the maximum "safe engine operating rpm". The tachometer may function all the way to 7,000 rpm but that don't mean that your engine will without blowing up.
Note: above taken from Shuboxchevy's thread back in 05/16/2008-how do you determine a redline when installing tach
I have seen blueprinted Z/28 302ci small blocks that were set up for professional racing cars that can and do rev to 7,000 rpm during shifting while racing, but I would not recommend doing that to a stock or daily driver engine.
Gary