don't know for sure on a 65 but my 68 is natural with Chevy Orange overspray where it mates to the engine

Found this one on ebay listed for 283 and 327 Chevrolet Bellhouising.

I knew this would happen to what seem like a straightforward question.

I wouldn't be surprised if natural or paint was specific to each manufacturing facility.

I know from hanging out with Corvettes this summer I see more painted than not.  

Here, a Muncie transmission is being installed into the back of a 327-ci Corvette engine and will be secured with four 3/4- inch bolts that need to be torqued to 70 ft-lbs. One person can do this task but it is much easier when a second person is lending a hand.

Thanks Guys/Ray,

Makes sense they were likely painted for the most part. Logic would dictate that the "manual" engines probably arrived from the maker with the flywheel, clutch, bellhousing and lever in place. I do know most engines also were set up specific to what trans they were to be used with, in that transmission specific carbs, distributors and aux equipment were paired according to the different types. When the builder fitted the manual type carb, would it not make sense that they also fit the clutch assembly at that point? Automatics are another story, as they could not be split for the most part...easier to pair them at the time of assembly? Talk of the overspray type paint.. they probably were mostly focused on the engine itself, as thats what one can really only see from hood up. Get a little or a lot on the bell and it's all good.

So paint it is...but not too nice lol!

Cheers

Looks to be tall deck Big Blocks. Pretty sure they have the extra bolt on the top of the bellhousing. 

The Small Block has an adapter plate for that heavy duty bellhousing.