A body 69 Thumb wheel in 69 R.R.?

not even close. when they made thumbwheel radios each car line had a different one. in 69, the dart, valiant and barracuda were all different. Even C-bodies were completely different amongst each other. Radios didn't start getting standardized till after 71 and later on some models.

The 69 valiant will have two tabs and that will never mount to a road runner dash.

You might find one to fit the roadrunner in a coronet with a standard dash. but then the faceplate will be different because a coronet radio will say "dodge solid state" which is wrong in a Plymouth obviously but will bolt up.