For the forward head ball valve removal, I carefully used an oscillating multitool, then a mini-hacksaw that has a portion of the blade sticking out past the frame and finally a plain hacksaw blade by hand to get the outboard most part as best I could.
I had a lot of difficulty getting my 16" adjustable wrench to get a good grip on the flats of the valve. It is clearly the wrong tool for this job. I switched up to my largest Channellock (20"). I put one jaw on the "stub" where the valve handle goes (with the valve handle removed, of course) and the other gripping the middle of the valve body (the round part, not the flat). It came loose on the first try with what seemed like a ridiculous amount of force. So much force that I feared ripping a hole in the boat. I imagine that a pipe wrench will also work well here as the serrated jaws will bite into the valve.
Here's a pic of the old valve on the left and the new Groco valve I replaced it with on the right. Note the copious amount of gelcoat all the way up the back of the old valve.
Oddly, the aft head had absolutely no fiberglass or gelcoat on the ball valve. It appears to be the original valve or if it was replaced by one of the three previous owners of Cara, it was replaced with the exact same type of valve.
SM #440 Cara
Annapolis, MD USA