Not to sidetrack your oil question, but to figure out which engine you have look at the short heater hose that runs at the front of the engine, between the block and the head. If it's about 2" long, it's a 170. If it's a little over 3" long it's a 225 (or possibly a 198 but those are not real common).
I have the original 225 in my 66 Valiant, somewhere around 128K miles. I run whatever 30 weight is on sale. I don't run the car in any kind of extreme weather. When it gets the new engine this winter, I will run 5-30 which is a good match for my part of the world.
