Synthetic Oil Improvement in /6

I really get nervous posting on oil threads....:pale:
My 225 slant has 93K on it, besides the carb needing rebuilt, runs nice and quiet.
I just got my latest one the other day. The tranny fluid is nice and clean, but the oil is a little dark.
I wouldn't mind changing out the oil right away for a starting point.
So you think running 5W/30 Blend or synthetic is okay? Just making sure!
I used to always run 10W/30, dino.
I have read so many oil threads.
Then I read we need the ZDDP for our older engines??
I get very confused.

Zddp is for the flat tappet cam. The oil out today lacks the higher levels of zinc in it because it messes up the cat in new cars. Understand full syn (maybe blend as well but I'm 100% on that) will find the smallest leak and start leaking a lot because syn is a lot finer than regular oil. Now don't get me wrong all of my cars run full syn Mobil-1, just letting you know.