Will a Merc 500 Bulldog 540" oil pan work well on a 4.5" stroke motor?
What other oil pans should I be looking at for a dart block?

I use alot of Stef's marine offshore pans. I am a WD and can get you a great price.

OEM Core pans can hit the the main caps on a Dart block. 4.5" stroke will require a pan with stroker notches. I would recommend taking Dean up on his offer and go with a Stef's Offshore pan.

Will the Stef's pan be able to be used with a Bravo setup as well as a Transmission setup, I would like to have the option to change drives in the future and prefer to use the bottom mount starter for now.

We can put a start notch on it no problem for a tilton style starter. Our pans are complete with welded pickup to a Melling pump and are test fitted for each application. Won't be a problem for what you want. Pan includeds the bracket for the waterpump, windage screen, and mounting hardware. Dean will take care of you.