If I was going to rebuild a choice between a '66 and a '69 383, I'd go with the better-performing '69.
One could use the better parts from the '69 on the '66 short block, though.

So with my car I am just looking for a cruiser and something that can take some beating on it. I'm not looking to burn the world down with it.

The car has a 23 spline and 8 3/4 4:10

The engine that is in it is a 1969 383 out of a Fury from a previous engine. It was a 2 bbl engine and was unknown . When I pulled the pan last time it was out, there was a ton of trash in the pan.

I figured the 1966 300 engine would be good because it was a factory 4bbl engine and factory dual exhaust. I have been reading that that engine was a 320 hp engine and has closed camber heads. I have a set of 67 440 heads (I forget the number) that I was thinking of throwing on there. I wasn't going to just slam it in, I wanted to do a very basic rebuild with a 440hp cam. I figured with its high level of maintenance there is a higher chance of the internals being good and reusable.

I really appreciate the advise and guidance. I really don't want the car down waiting for the block holding down the machine shop floor.

the first thing i would ask, is what are your driving habits, and what are you truly looking for in an engine ?
if you just want a sweet cruiser, and the engine from the chrysler runs as you have described, i would just re-gasket and replace the core plugs, do what is needed to address using your transmission, install your intake and exhaust manifolds, then install and run it.
that would amount to the shortest down time, and you would once again be enjoying your car.
if you want something else out of the engine combo, the above may still be the quick answer, allowing you to search out other options, while still having fun.
or be like me. let car sit while working on other's cars and collecting parts for mine. get health issues preventing me from working on my car while still working on other's rides, get old, and wonder why i'm not beating on my car.

This motor may not be drilled for a pilot bushing. So if you have a 4 speed that is going to be an issue.

the only difference are the pistons ... taller CH that would actually work better with the closed chamber head .... and the heads ...a little better flowing ... and the intake with the bigger carb base pattern .

When doing a rebuild all those parts get tossed usually.