I have a gauge overlay where the tach reads 8k, will this work seeing as the stock limit is 7k. Car is completely stock, no engine upgrades or anything..that I know of...
Also, my gas gauge stops at 1/4 tank all the time, never goes below it...what should I try to do for that?
As for the first question, no. You have the overlay for the 96-98 Mustang, with the higher revving 4.6 engine. If you use that overlay, your tach reading will not be accurate.
About the fuel gauge- my first thought is that your float is sticking. Take the tank down and check it out. Others may be able to provide a different solution, though.