1). You can just use a Tee at the transom, but use a valve on each side. They will draw together, but usually not equally, and you might run out of gas and still have a 1/4 tank on one side...close empty side and head to the gas dock.
2).Surge brakes I suspect- If the 'bore' in the master cylinder is good, get a rebuild kit, bore diameter should be on the plunger/piston- 1 & 7/8ths, etc. the older drum brake shoes were mustang, 9" dia. x 1.75" or 2"
I think like 64-68 or 69. There are kits to upgrade to surge disc brakes, or even electric drum or disc brakes. Kinda depends on your budget and your tow vehicle, if you even need them, but I tow with a dually.
3). What RPM were you running before the build of the motor? and after? where do you WANT to be? You would be surprised at how well a 'fresh' performs over a 'loose' pump.
Refreshing a pump is pretty simple, might need an impeller puller and some gaskets. A pump will absorb whatever horsepower you're willing to throw at it...think dyno. Some shops- no particular order- MPD-Costa Mesa, GS Marine-Corona, B-1 Racing-Anaheim, I think
Dan'l