When you convert another game's setting, adventures, crunchy bits (equipment, monsters, etc.), or game elements (sanity checks, etc.), do you:
- convert them with maximum fidelity to the source rules?
- convert them with maximum fidelity to the end system's game rules?
- just pick something from the end system's game rules that fills the same need?
- convert in some middle ground kind of way?
For example, we're playing Gamma Terra. Gamma World has a random level up bonus chart, so our GM made up a GURPS-compatible version of it. When I ran GURPS 3e based Gamma World years back (my "Mutants & Mayhem" game), I didn't convert that - you just earned points like you normally do in GURPS.
For weapons, we've already seen some very Gamma World-like weapons, like Torc grenades. In my game, I just ignored most of the Gamma World weaponry and instead picked similar devices from GURPS Ultra Tech and handed them out. Where GURPS lacked something I felt was necessary, I just put it in and found something similar to nick the stats off of.
Rules like mutation, radiation, etc. I ignored and used GURPS rules instead.
I've done similar things in other places. I've converted a fair amount of D&D monsters to GURPS in my day. Back in my first games, I often directly ported effects over. 50% Magic Resistance? Roll percentile dice, see if the spell works. These days, I'm more likely to say "Magic Resistance works like in GURPS." My old, old sheets said stuff like "+1 Puissance or silver to injure." These days, more like Accessibility-limited Damage Reduction. When I did a pirates game that was based on a game and setting that had primary, secondary, and tertiary characters, I just did 100, 75, and 50 point characters. And of course when I ran AD&D, "converting" D&D monsters was as simple as just not using the Morale stat and adding "evil" to the end of Chaotic on most alignments.
I'm curious what other people do - I'm sure for most it's a mix. But what do you favor? Pull the mechanics for, say, Sanity right out of Call of Cthulhu and use it bolted on to your system? Change it to something that fits the resolution in your home system? Ignore it and make up a new rule entirely? Pick one that's close enough?
Conversion is a funny thing - what you demand out of them can be very different from another GM. And what you get by the decisions you make can change the flavor of your game immensely.