2 preval sprayers should be enough to do a whole engine.

Buy one with the spray unit and the glass jar, and a second spray unit. Probably $16.00 +/- for the pair. Once you have the glass jar you can clean it with reducer and reuse it over and over.

I use them for priming small items all the time. Best thing is the air pressure is relatively low so you don't end up with a fog of overspray that gets all over the place.