"Working by feel" is kind of a fact of life with the small engine rooms implied by twin gas powered V-8s. (If the boat were smaller they would not fit, if it were bigger we would have diesels.) If you find you cannot get it done laying on the engine and working by feel, their are several steps to consider before pulling the engine. In my case the problem was an oil cooler stuck low on the hull side of the block but the answer is likely the same. You can remove the alternator to create some additional space. Next try draining the coolant and removing the exhaust manifold on that side. That will give you even more room. Finally, just pull the head. It is amazing how easy access to side of the block becomes once that is off!
Of course now you are looking at new gaskets for the elbow and the head and if you are going that far you should send the head out to be flattened and get a valve job. And since the intake manifold and everything associated with it are already off and the coolant has been drained, it is a quick job to pull the head on the other side and get a valve job there (got to make them match!). And if the elbows are anything close to due, since they are off you can put new ones on both sides as well. You will also find the job easier if you put on new exhaust hoses as the old ones will be really stiff and cracked. Then, of course, the same stuff will look to need doing on the other engine, either right away or on next year's to-do list. Ain't boating fun?
The whole thing reminds me of the time I ended up gutting and rebuilding a kitchen that started when wifey said "Honey, one burner on the stove is not working."
Oh, and be sure to bring down a small rug or piece of carpeting to lay across the engine and provide some comfort when you are working. That was the most important lesson I learned in doing this fix.