When making changes to a car engine it is important to have a diagram. The 1992 Ford Mustang Engine diagram can be found in its maintenance manual.
http://www.veryuseful.com/mustang/tech/engine/
The compression on a 1992 Ford Mustang 5.0 is 9:1
.054 inch
Your 1992 Ford Mustang GT has the 5.0 liter V8 engine with dual exhaust so it has ( 2 mufflers )
According to fordparts.com the 1992 Ford Mustang with the 5.0 liter V8 engine takes the ( Motorcraft FA-1042 ) engine air filter
A diagram should be affixed to the underside of the hood, toward the front, and on the right side.
( .054 inch ) according to fordparts.com for the 5.0 liter / 302 cubic inch V8 engine in a 1992 Ford Mustang
The 1992 Mustang LX 2.3 liter, 4 cylinder engine had an increase of horsepower to 105 due to two sparkplugs per cylinder. The V8 model had a rated horsepower of 225.
According to www . ford parts . com ( no spaces ) The spark plug gap for the 2.3 liter four cylinder engine in a 1992 Ford Mustang is ( .044 inch )
The compression ratio on a 1992 Ford Mustang GT 5.0 liter was 9:1
Mustang Electrical and Vacuum Diagrams Try the links listed below.
I believe Ford started using the 4.6 liter - SOHC - V8 engine in 1992 in their full size cars ( Crown Victoria etc. ) but didn't use it in the F-150 until 1997 and the Mustang until 1996