Depends on the feel you’re going for.
If you’re just wanting to unify magic as one thing, then use the best. That keeps the feel ‘default DND’; and spell choice for a sorcerer becomes personal preference or ambition rather than class choice.
As Alex intimated, if you’re looking for a more solid S&S flavor, rebuild at the worst.
Fireball, for example, is 2721.20.75(1 arcane) = 49, technically 4th level, but third because the breakthrough version is the common version. At divine costing, it’s 110.25 - assuming the same breakthrough, it’s a 9th level ritual.
That’s a big change. Heck, even Magic Missile goes to 3rd level (10*2.25, 22.5) if barely.
Cure Light Wounds moves to 2nd level at arcane pricing (x1.5). Restore Life and Limb hits 7th, I believe, and Cure Poison is 6th.
I’d expect you’d be left with mostly utility-style spells at 1st level, maybe even 2nd, if you went through them all and repriced them all at their opposing worst multipliers.
One other common alternative is to penalize casters who use spells that ‘break’ the S&S mold - single them out as spellcasters using magic of an especially heinous source. Crypts & Things does that as a modification to the base Sword&Wizardry; DCC does it to everybody, and the post on my blog after the one I linked presents a conversion of Mongoose’s d20 Conan Corruption rules that ties back a little into ACKS’s various Mortality tables for using spells that break that mold.
That being said, it’s not an easy thing to do, combining the S&S feel with Vancian casting, and I’m not qualified.