Well, I finally got both tow valves installed after quite an ordeal. On the starboard side I removed the black intake hose from the back of the "y" and installed a brass burred fitting in that hose and then connected the other end of the burred fitting to an 8' hose that I ran under the engine and back to the "y" fitting--like
paul075 did. The new hose looped at the front of the engine so I cut it there and installed an Island Racing "tow valve". The main thing that caused me a problem was that I couldn't get the spring clamp off the intake hose--I must have spent two hours trying different tools until I finally managed to get it off.
I had so much trouble with that clamp that I bought a tool with a flexible extension to reach the spring clamp on the port side but it wouldn't do the job. After struggling with the port side clamp for an hour I removed the red flushing hose on the "y" and cut the black intake hose just before it was connected to the back of the "y". Once I did this I was able to wiggle off the spring clamp from the "y" without too much trouble.
Now I had the black intake hose just laying on the bottom of the boat under the clean out tray so it was much easier to work with. I installed a burred fitting in this hose, then laid out the looped hose in the engine compartment, going around the engine on one side, and was able to connect the new hose to the burred fitting and the other end to the back of the "y" without much of a problem. Then reconnected the red flushing hose back to the "y" and installed the Island Racing kit in the front of the looped hose.
The whole process took me several hours because I couldn't get the spring clamps off the intake hoses and the difficulty of working while lying down on top of the engines. If I were to do this again I would remove the red flushing hoses and cut the intake hoses behind the "y"s instead of trying to get the spring clamps off. Also, getting the burred fitting into the original intake hose was so difficult I had to wet the hose with some Deep Creep to be able to push it in. The fitting wasn't a problem with the new hoses, and the new hoses easily connected to the "y"s. The only other issue I had, which was minor, was that the clamps supplied by Island Racing were a bit too small to easily fit over the 5/8" inch hose I was installing. I had some larger clamps with me so instead of fighting with the smaller clamps I used the larger ones.
I'm glad this is done but if anyone wants me to install the tow valves on their boat it will be $1000, per engine.