Hy Troy1950, welcome, there were no stock 235/261 heads that I'm aware of that were machined for taper seat spark plugs [5/8" hex], by the way both the washer type and taper seat plugs are 14 mm thread. The polarity reversal switch was a device they came up with to limit metal transfer from one side of the points to the other, every time the engine is started the electrical polarity travelling through the coil/points was reversed. As to the oil, you will get many opinions, the technology of the day was 30 wt. for summer or warm climates, 20 wt. for winter or colder climates. Modern oils are much better lubricants, and most reports I have read say 10/30 is the best lubricant for most applications. However of late most oils have had the zinc level lowered to the extreme, zinc is needed to help lubricate our old flat tappet engines, so you might consider the new oils that have shown up on the market specifically for flat tappet engines, hope that helps.
