Building a bike from the cranks is really the only sensible way to go for tall riders.
Long cranks set the bottom bracket height for pedal cornering clearance, and the front-centre dimension (bottom bracket to front axle) to avoid toe clip overlap with the front wheel. Long cranks also solve the issue of saddle layback (horizontal distance from pedals to saddle), so you dont require a really slack seatpost angle to get "knee over pedal spindle"
Does the Gunnar have the correct BB drop and front-centre for your chosen cranks?