Here's some other proposals for Engineer and Magical Researcher.
Engineer: Karl Sonntag (Or is that Carl Soontag?), from Mechwarrior 4: Vengeance.
While MW4 was pretty disappointing in terms of game mechanics, Karl seemed to be a very competent technician and engineer. With his team of technicians, he was able to repair 'mechs within a reasonable timeframe from various damaged states, refit and reprogram IS mechs to use clan weaponry in a snap, and scrounge and salvage enough components to repair 'mechs of all sizes and shapes (he was only supplied by whatever Ian Dresari's resistance force was able to plunder, which may be a mark in his favor as far as efficiency goes). After the events of MW4: Black Knight, he doesn't seem to be doing much of anything.
However, he seems to be rather judgmental for an engineer/technician. If we get to a point where we really do need to do evil or morally questionable stuff to enforce canon, he may refuse to work for us.
Magical Researcher: Psoron, from the Valkyrie Profile series (VP2).
While his role in VP2 is a combat sorcerer, his true profession is that of a magical researcher. His work on two very basic offensive and defensive spells were used as the foundation for entire schools of magic in the mortal world in his canon. In addition to being a minor character, his revival from Einherjar to a mortal being occurred waaay ahead of his first mortal life. Thus, it may be easy to recruit him and not mess with the canon much, as he was first introduced after he already made his mark on history.
There are potential downsides, though. First off, we cannot know if Psoron was actually encountered and revived in canon; all the Einherjar you recruit in VP2 are randomly generated. Secondly, while his work had a huge impact on his world's use of magic, this does not necessarily mean that he will be all that great in comparison to the other choices we have.