Will a 68 GTO hood tach fit a 68 Firebird hood?...Are the mounting holes on the hood the same for 68 GTO's and 68 Firebird's?...Also, what would the correct rpm red line be for the 350?

I'm not quite sure, but I would think they would be much the same? They may differ slightly, but perhaps not enough to notice?

I think the main difference was between the OHC-6 tach and the V8 Tach? But I'll let others who have the info handy tell you for sure...

Brett - 67 Drop Top 455!

I believe you will want a 5200 RPM tach, the 5500 was for the ram air engines I believe. The other issue is 67/68/69 had slightly different units, both background color and overall height.

My 68 project Firebird with the standard hood has the cutout for a hood tach but the tach was not included. I don't know if the cutout was done by the factory or the dealership, but it does look professionally done and I just need to know if the mounting holes are the same for the GTO and Firebird hoods. I don't have alot of cash but I noticed that Original Parts Group has the GTO hood tach's the cheapest @ $189.95 It doesn't matter to me if it's not 100% correct, as long as it fits in the hood without any mods.

The only differences that I am aware of are the 67 tachs were taller than the 68 and 69's. The lower profile tachs came in 68.

As you mentioned... a 68 GTO Hood Tach "should" fit a 68 Firebird hood tach hole... I would think?
Again as long as it's apples to apples type of thing. So any of the V8 GTO hood tachs "should" work...

Brett!