Which type of oil to use

1971 CY Dodge Dart said
No way would I run 20W-50. 10W-30 is a good weight oil for most climates/usage/builds.

The ONLY reason I tried it was because I already had it and she needed an oil change. It's funny. The spec on the T18 4 speed in my truck is 50w motor oil, so I drain the old and used the 20/50 in there. Works good.