If you don't care about correctness, concoursness (Jim, is that a word?) and other nesses, you can delete the valve. After all, cars without AC don't have them, right? In modern terms, the valve is a "A/C max cool" function.
A car that originally had factory AC would take a lot to completely remove all parts that are part and parcel of the AC system. You've mentioned a few things (water valve, vacuum tank vacuum hoses) that you still have. I would guess that you have the AC plenum, AC duct/vents, AC control panel, and other AC gobbly gook under the dash. If you leave the vacuum line to the heater valve hanging like a chad, when you move the cable operated blend door position to full cool, a vacuum switch (which is one of the items probably still under the dash) will port engine vacuum to that hose, so you will want to put a cork in it - figuratively.
It is a challenge to determine where to stop for something like this. Jim referenced "the future", so you might want to consider someone down the road that might want to undo the voodoo that you will do. So if you remove the valve and bracket, put that and the mounting screws in a quality zip lock bag or box, with label and keep it in a place to remember.
To reiterate - the valve does not "turn off the heater" per se. For AC cars, on max cool, it will interrupt engine coolant flow to the heater coil...if everything is working correctly after 50+ years. On cars without AC, which is what this car effectively is at this point, when you move the blend door to full cool, it is bringing in outside air through the cowl vent. There is still hot fluid going through the heater coil. With imperfect seals, some of that heat will leak by. The answer is to shut off the blower and open the windows. Heat still circulates through the heater coil.
