- Check the upgraded version's level and stat requirements on the white items webpages:
Long Staff --> Quarterstaff (Lvl48, 53Str, 10Dex)
Skull Cap --> Sallet (Lvl45, 61Str)
Studded Leather --> Trellised Armor (Lvl48, 63Str) - All mods from the basic item remain unchanged, but might gain effects from the recipe:
Upgrading Basic Set Hat gains +1AllSkills, +5PDR/MDR
Upgrading Basic Set Armor gains +5PDR/MDR
Upgrading Basic Set 2Hand gains +2AllSkills - For stats like damage and AC, most mods related to those in v1.7 just double them (+85-100%), so they are pretty easy to figure out from the white items stats. Note that upgrading an ethereal armor is bugged in D2, and you will lose the ethereal bonus (the item remains ethereal and irreparable, you just lose the extra AC). If that armor were rare, then rerolling it with a glyph will regain the ethereal bonuses when it gains new mods.
That should be it. If there were extra level or stat requirements added in, then the cube recipes page would mention them. I suppose one oddity is that there are 4 tiers of Circlet, but my solution was to just treat Coronets as an exceptional item when you're upgrading Circlets, but also as a basic item that upgrades to Tiara (Exceptional) and then Diadem (Elite).
If you're not super concerned about exact numbers, then I generally added 40 to the level of a basic item when it becomes Exceptional, and it's Str/Dex requirements are probably very similar to other items of that level and equipment type (light (e.g. circlet, quilted armor), medium (e.g. skull cap, studded leather armor), or heavy (e.g. Hard Leather armor, Full Helm)). About 50Str is needed for all end-game Light armors, 100 Str for all end-game Medium armors, and 150 for end-game Heavy armors. There's more variety among weapons, but they're generally similar and might have some of the stats split into Dex requirements.