About your pump: I use the ABP pump from SubTech. It's a high volume pump, pretty small, and perfect for the job.
(It fills a 1L bottle (App. 1/4 gallon) on just 15-20 secs.)
About the engine: Have you looked at Graupner engines, eg. the Speed 600BB? It's perfect when used with a 3:1 gearing.
Graupner engines are good, just remember to buy one with the "BB" designator. "BB"=Ball Bearings. They come in voltages from 4.5 to 14V=
Please see my site for more info on the engine and gearing, and the link to SubTech.
Yours Sincerely, Robert Holsting, Denmark
1/81 SSBN Ohio Class scratch builder, more at www.robse.dk
"Never be afraid to try something new; remember that it was amateurs who build Noah's Ark, and professionals who build the Titanic"