In this game I won a tower-victory with orc-engineer and overseer, spending no single brick (at least not for my castle).
IMO This new engineer is too strong... not only does it work great as finishers (you need no bricks, no need to worry 'bout the quarry lost), you can even "clone" them with halfling rogue several times, so it's probability to come up can be even higher then a common card (including one turn to "clone" it).
Maybe it's power can be decreased by including an "if-clause".
E.g:
Tower: +7
If Quarry>1: Tower: +10
Quarry: -1
Same proposition for Overseer.
If these cards are too weak then, go and switch the tower-gain... or increase tower by 25 if quarry>1