what oil and plugs?

[Mr 5 0]

I've used petroleum-based Mobil 10-30 for 111,000 miles in MY '90.0 LX (bought it new).
Never had a problem in 11 years.

Synthetic oil is superior but you pay a high price for it and some Mustangers have had seal leakage problems they never had before when switching to synthetic. Others have no problems at all. Hard to predict.

On your older, 79,000 mile 5.0, I would recommend using 'regular' oil and changing it (with the filter) every 2,000 miles, as I do.

For spark plugs, I use AutoLite #25 copper plugs. Cheap and reliable. Recommended.