If you can, get SM:P.
The work to be done involves arranging skill categories and skills. My end result was non spell users had an advantage on developing both mundane and sci-fi skill sets. Spell users are forced to be much more selective on the tech they can master,
Spells and tech are similar, with tech having the definite edge at low levels, particularly healing. Tech is also more reliable (considering fumble and break factor ranges). Tech healing is far more useful and easier to access, a big help in any world with slug and energy projecting weapons.
Ten Million Ways to Die will give you all the attack tables for modern and sci-fi weapons along with SM armor types/attack tables for melee weapons. Some really neat melee weapon attack tables are available in the various SM companions. The chainsaw and vibroblade are favs of mine.
Believe it or not, the easiest way to work a mix of the two systems is to create two character sheets and use them as one...note, I use a leveless approach, so many of the problems of meshing the two games are replaced by a whole new series of headaches. Sigh.
Adding bonuses can be a problem. I allow one tech mod, one magic mod, one stat mod, one skill mod, etc. A targeting eye sensor that provides a +25 OB stacks with the rifles +15 superior design bonus, but not the +15 acuity sensor. Androids and cybernetics can get out of hand quickly without a strong guiding hand by the GM. If you ARE going to fight the Brood, even that will probably not be a problem as the Brood is badass defined.
The easiest way is just add SM weapons (TMWTD makes this very easy indeed). Add a few new skill categories to cover SM lore and science skills. I do not use psions. Generic assignment will have all professions paying the same for these new categories (2/7, 3/7, 3/9, etc).
We once tried to tie the cost of skill dev for mental and physical skills based on stat range. Every PC and NPC would have different skill cost based on their innate statistical abilities. It was SO overdone and complex. Worse, it really drove players to WANT high stats. ANyway, I only mention this to inspire simplicity. It is easy to overthink it and make it far more complex than is required.
Good luck.
