ST+DX+HT = P TRAIT
IQ x 3 = M TRAIT
120 - (P + M) = S TRAIT (if starting character, see below for other options)
Note on Spiritual TRAIT: You can (and probably should) select this with an eye towards the way the character has been played so far, realizing that faith, intuition, belief, and artistic abilities are typically summarized in this TRAIT. Also, the exact P and M formulae should probably add an average of 5 points to the combination, just to be fair and accurate.
However, if you are attempting to convert a GURPS sourcebook, then take the suggested character types as Vocations (using the recommended skills as the K/S Bundle). The K/S Area values should be: 30, 25, 25, 20, 20, 20, 20, 15, 15, 10, in order of importance, selecting the appropriate TRAITs to base them on.
Then, take the skill list from the sourcebook, and use it as a basic list of the K/S Areas available in this new, hybrid game.
The advantages/disadvantages probably ought to be ignored in Prime (the whole idea is simplicity over completeness). Equipment should be converted to a rough equivalence, realizing that 1 point of any of the attribute scores in GURPS roughly equates to 3 points in Prime. Weapons are much harder to manage, but a rule of thumb (not necessarily very good) is: (1) any weapon with an equivalence in an already established Prime system can just use those stats; (2) any hand held, non-projectile weapon probably causes 1D6 points of damage, plus 1D6 for each plus after it; (3) any projectile weapon causes the listed damage in D6, *except* area-of-effect weapons (wide-bean laser, sawed-off shotgun), which should gain an exposure roll on the listed D6. Yes, that brings these weapons in line with the deadliness they should have.
Anything else that is unusual (netrunning, magic, spaceship piloting, etc.) should be interpreted by the GM as best suits his/her purposes and fits in with the general rules framework.