140/5 mixed with 170/190 would seem pretty ambitious as the flight decks seem to be quite different. Decades ago we did Dash 7/Dash 8 and Dash 8/Fokker 50 mixed which seemed "doable" at the time and did not even require double proficiency checks for the Dash 7 / Dash 8 combination but I still remember our flight operations manager's finger spiraling around the overhad panel until he found the right button. It's probably a bit easier if you fly lots of sectors like we did on the turboprops. Couldn't imagine to do it on LR types where you'd maybe have two flights each.