Hi Mike,
Can't blame you for wanting to install a wiper.
A drawback with vacuum wipers is that when one gives his Model A the gas to pass a car, the vacuum wiper enters into a coma & stops .............. until one lets off of the gas whereby it starts wiping again.
However, after thinking about driving in the rain without a wiper, then possibly getting in an accident, (whether my fault or not), I thought how a judge or jury could have a blast pointing fingers at someone negligently driving in the rain without a windshield wiper .................. right or wrong, "no" wiper is as much a No-No as driving with no brakes.
Hence, I re-installed the working 6V vintage aftermarket wiper that came with my Town Sedan only because I thought ............. at least I would have a working vintage 1930 wiper.
Next, after trying this 6V wiper in the rain, (& also formerly having tried several Model A vintage vacuum wipers), I think it would be more effective to place & tie a dog on the hood & let him wipe the windshield with his tail while he ate dog treats.
Per Mr. Glenn's reply # 3, (& as previously mentioned often), "Rain-X" works exceptionally well when provided in strict accordance with the manufacturer's instructions.
Just hope this second-the-motion on "Rain-X" helps anyone to see better & prevent accidents while driving their Model A in the rain ................ besides when the dog treats get wet, the dog may stop wagging his tail.