Where do i look for a strong aftermarket coupler to buy,has to handle at least 600hp or are the stock ones that good?i have no problems with my stock one but having some power now and not even knowing how old mine is,makes me wonder.maybe i should replace it this year while engine is out for a cam swap.

Call Dino at Teague Custom Marine in California..this is where I got mine as well as my flywheel for an internal balanced 540.

There are 3 kind of bravo couplers-crappy design that had aluminum splines-they strip in stock bbc boats around 200 hrs
steel spline std bravo couplers-I ran one for a few years with over 600 hp,as long as you grease them and keep your alignment good they last ok
575 merc style-they are steel and have a long snout that supports the input shaft real well-I been running one of these for 6 or 7 years with as much as 1050 hp,it still looks real good. Almost impossible to have bad alignment because the drive will only go on if its almost perfect,Smitty