I really don't think choosing an interesting spray can color for one's personal engine is any sort of attempt to mimic another's engine manufacturing reputation.
That is because your mind is not as twisted as mine is. I think I have heard old time mechanics grumble about it but that is hardly evidence for an ethics debate. In any event, it would only be a concern from grumpy old mechanics who have been in the business for too long. Did Universal really paint their engines in all those colors or is that aftermarket/shade tree mechanic stuff?
I think any good clean color is a vast improvement and will show up any leaks pretty quickly. Curiously, black is often known as the color that shows dirt/oil the quickest. I definitely wouldn't be painting a new engine just for better color though.
Jason, I wouldn't worry about priming the engine first. Especially as you are thinking of pulling it because you are probably going to redo the paint at that point again anyway. Most auto parts stores have paints specifically designed for engines and come in original manufacturer's colors (i.e. Ford blue, Universal gold, etc.) I bet if you stopped by a John Deere dealership/parts shop they would have some paint you could use.
I can't remember painting an engine before but I am pretty sure priming is not a part of the process. Just make sure the engine is as clean as humanly possible (which should be a standard goal anyway IMHO).
Once the engine is painted you should send in a picture to Moyer. They are starved for monthly pinups.
-Britton