It sounds like you probably have already installed the deck. If so, that is an arguement against moving the front deck beam or installing a second one.

I can't see any problem aligning the rear of the coaming with the rear deck beam and letting it overhang the front deck beam by an inch or two. Put a little brass ID plate with the builders name, boat model, owner, etc. on the portion of the deck that protrudes into the cockpit. No one will ever know the difference.

Installation of the coaming is a little tricky under normal circumstances. So why cut down all the pieces and create another opportunity for error?