I am debating whether to keep the 289 that is coming with my 65 coupe, or putting something else in. What size engines will fit in the engine bay with no modification to the shock towers? What size engines do most of you have in your Mustangs? The reason I may not keep the 289 is I am not sure if it runs, and I would really like to have some street power like a 351 or a 347. Also, what transmissions are compatable with what engines? And if all are, what does it take to connect them? Different bellhousing? Thanks for all the help, I know you guys know what you are talking about.