I think they've said there aren't any plans for rules to convert back, but give it 6 months and someone will come up with some I'm sure!
It'd be fairly easy to drop the weapon specialization +Char level dmg bonus everyone gets.
For the most part KAC/EAC is close enough that you could take their average. Maybe reduce a little bit because Starfinder doesn't use shields, and feels like the basic KAC/EAC compensates for that.
So take an iconic like Merisiel at level 12. +5 studded, +2 buckler, +2 ring protection plus her Dex of +5. Overall ends up with a AC 29 (Base 10 +19)
A level 12 starfinder in Light Armor (if only access to level 12ish armor) is average +13 to +15 for both EAC/KAC. Then adds bonus due to dex.
Valerous as a level 12 Fighter has the same AC. He's also functionally a 'light armor' user.
Actually even the heavy armor types in Pathfinder (iconics) tend to have this rating since their Dex bonuses tend to be less.
Roughly speaking KAC/EAC for heavy armor is about 2 points higher than light at the same level. So overall maybe don't need adjustments on AC.
In terms of hitpoints, I feel like you twice the hitpoints (plus stamina) that you do in starfinder, but also kind of evens out because the weapon damage is about twice or so (it varies based on type of weapon) the dmg output of a same level pathfinder char.
So an easy thing would be taking the average of the Starfinders Stam + HP and making that their pathfinder HP value, and halve the dmg value of the starfinder weapons.
As for weapons themselves, I dunno. If we make starfinder weapons ranged touch for energy weapons, this makes them a bit more potent (hit more often) than if they were actually back in starfinder. So it might be better to just make them 'regular melee or ranged attacks' rather than any sort of touch attacks.