What makes a motor?

Cooling, fueling, electrical and mounting... plus bellhousing.

The stuff I'm gonna mention pertains to Small Block Fords

One component that doesn't get much thought given to it is the timing cover on SBF engines.

Depending on who marinized the engine and how the raw water pump mounts you'll find differences in the covers

You're learning right about the thermostat housing too Dave.

Not just any old flywheel works either and there are variations on the starter noses so the starter, the bell housing and the flywheel all have to be compatible.

Most use a 157 tooth flywheel and a long nose starter with the marine bell housing.

Holman Moody conversions are an outlier as far as starter, flywheel and bell housing

You'll also find different distributors, mostly Prestolite and Mallory but some Autolites were on 60's and early 70's engines.

You might find a Holley or an Autolite carburetor on early SBF's too.

For you Dave, you might find an Edelbrock that somebody threw onto an engine sometime over the years

Different brands of alternators/voltage regulators come to mind too

I'm sure the list could go on, but that's what comes to mind right now

Gary S wrote: I wonder how many here have noticed this on their Gt40 engines?

I have!