Question: Using D20 Stats with GURPS Character Creation

[Elliander]

I am starting a new campaign where, for the setting I designed, we have decided to use GURPS as the base for overall Character creation, but we are going to be needing to use the base stats that are used in D&D. We are also going to be using a Spell Point system, a D20 Magic system, and we are going to be using a Shadowrun Movement point system.

With the exception of NPCs that I will be creating, the vast majority of monsters will be using Pathfinder stats which is why, for simplicity, I will want all of the players to have comparable stats.

So here's my basic question: How do D20 stats convert to Gurps stats in regards to character creation? From what I can tell, in Gurps, players choose their stats instead of roll them. Is there even a point at which characters "level up"? (and in that regards, how would I use a D20 spell system without having levels as a base line, unless players also choose caster level with points as well?) If I convert the stat function and use GURPS stat costs, what is the base line for figuring out what level the characters are to select an appropriate D20 opponent?

From what I can tell:

ST = Strength
DX = Dexterity
IQ = Intelligence
HT = Constitution
WILL = Wisdom
Per = Perception = a D&D Skill
FP = Fatigue = Non-existent in D&D

And Charisma appears to be non-existent in Gurps?