50 ohm coax to each antenna should be 1/2 wavelength
phasing line should be 72 ohms 1/4 wavelength
spacing between dipoles typically could be 1/2 wavelength
you could set up a simple ratio using existing data to get into the ballpark for spacing:
33 ft/40M =Xft/17M
X=~ 14 feet
If you have trouble calculating dipole dimensions, use this:
https://www.omnicalculator.com/physics/dipoleThe problem you might face is that the dipoles are balance antennas and you're feeding them with unbalanced lines so it's conceivable that you could get antenna currents flowing back over the coax shield. This might require tweaking of the dimensions and proximity to other objects.
COAX CABLE VELOCITY FACTOR: The velocity factor of a coax cable is important in applications where phasing of signals is important – phased antennas, matching stubs and many other applications need a knowledge of the velocity factor.