FoxFordCatGuy12

Wrong, the part number for famous chrome 5.0 fender starts w/ "D9ZZ". In Ford speak "D9" indicates 1979 - the 1st year it was used. (D=1970s, E=1980s, C=1970s, etc. D + the following number [9] = 1979.) As I said, it was first referred to as a "5.0" during the Mustang II years. The "HO" designation started in '82, but "5.0" was around years before. '82 HO was the 1st year the 5.0 used the 351W firing order (1-3-7-2-6-5-4-8) b/c it used an early '70s 351W camshaft. Non-HO '82 & up 5.0 still used the old 289/302 firing order (1-5-4-2-6-3-7-8). '82 & up 5.0HO used the 351W firing order. That is a key reason for the HO designation, to diffentiate it from the base 5.0 which had a different firing order. [IIRC at some point in the '90s even base (non-HO) 5.0 got the 351W firing order. My '92 5.0 F150 is still old 289/302 firing order.]

Transmission type had no bearing on which seats the car could be ordered with.

Yes, T-5 5-speed became the standard manual in mid-'83. But the 4-speed was still available & came with a $124 credit.

Didn't say it wasn't. I said the 4.2/255 was the only V8 available in '80-'81 & the 5.0 returned in '82 (with manual transmission only. '82 automatic trans cars still got the 4.2).

The 5.0 in the '82 Mustang GT was rated at 157HP w/ a 2V carburetor. Quicker than the '82 Camaro which had a 4V & was rated at 145HP.

That is a '79-'82. '79 5.0 was rated at 140HP. '80-'81 the only V8 available was the 4.2/255 rated at 119HP in '80 & 120HP in '81.

Ford started using "5.0" on the Mustang Cobra II. It had "5.0" decals on the hood. The famous chrome "5.0" badges debuted in the '79 Mustang. '82 was the first year it was referred to as "5.0 H.O."

The 255 was the only V8 available in '80-'81 & in '82 if you wanted a V8 w/ an automatic you got the 255/4.2. The 302/5.0 was available in '79, '82-'83 w/ manual trans only ('83 V8 Mustang was only available with a manual trans) & '84-'93 5.0 was available with either an auto or manual ('84-'85 5.0 were lower HP CFI, '84-'85 T-5 5-speed were 4V carburetor.) '87-'93 did not have amber rear turn signals. Only '83-'86 & '93 Cobra had amber rear turn signals.

The '82 5.0 HO in the Mustang GT was rated at 157 horsepower.

Only 255/4.2 was the only V8 available in '80-'81 Mustangs. '82 automatic transmission cars still used it as well. '82 4-speed cars got the newly returned/upgraded 5.0HO.

'84 would have come with a 5-speed from the factory. The T5 5-speed replaced the 4 speed in '83. In '85 the T5 was upgraded to a "World Class" T5.