So, emptied and started to take out the gas tank but was able to avoid fully removing it by having my wife assist me.. her slender arms were able to fit through the exhaust ports on the back down into the bilge to grab the hose as I fed it behind the gas tank, after shifting it forward enough to give us some wiggle room.. doable that way, but it was still a pretty tight fit.

For future reference, the exhaust hoses on the top of the transom are set up as follows: The two outside hoses simply drop a few inches, then loop up and are screwed to the transom to passively let fumes from the area around the gas tank vent (I assume). The two inside hoses are the ones that drop down and run under the gas tank to the blower motors. I was missing one blower motor, so I've replaced that. Now just need to run a little bit of hose from each blower up under the engine, then replace the front vent hoses (one behind the dash, one behind the observer seat) which have also deteriorated, although not as bad.