"As I recall....regular leaded gas"
Well, the leaded "regular" of yesteryear was of a higher octane than the
unleaded regular of today. Matter of fact, the early
Sprites (8.3-1) ran fine on 94RON, with
98RON (or better) specified for the later "H" (8.9 or 9.0-1, whatever) motors.
Thus....with the early 948 8.3-1 motor, use
at least today's "midgrade" or 89PON. With the later "H" (8.9-1) motor,
"hi-test" of as high an octane as you can find. Sunoco/Cities Service pumps
as their normal hi-test with Sunoco making
94PON available at an extra 50c or so a gal.
The foregoing hi-test octanes aren't avail
in some locations that limit premium pump
octanes in accordance with local and/or state law, ordinance, whatever.
Add no more than 3 numbers to PON to
come up with a ballpark equivalent RON.
For the "H" motor....
If you've only 91PON around, you may have to retard the timing a couple of
degrees from spec. to avoid a little pre-ignition/detonation in hot summer
weather. Or run the "rich" needle given
in the book....."V2".