72 350 and TH350 troubleshooting?

[Dead Parrot]

Keep in mind that the t-stat starts to open at the listed temp. Running temps will be ~5-20 degrees higher. Most SBCs came with a 195 t-stat.
Either get used to gauge quirks or try replacing and get stuck with the 'match the sender to the gauge game.' Lots of threads on that particular game. Changing the t-stat temp on an engine with proper operating temps isn't a good idea.

Might not hurt to clean all of the gauge connections but that requires digging into the gauge cluster. 50+ year old connections can get dirty.

Transmission - Being a bit slow to shift into reverse could be as simple as low fluid level or a filter that needs changing.