Adding to the poo flingin', IMHO vac sec's would work good on a TR....Especially if shooting a little over on bore size to begin with, venturi selection may be tricky... 
GT
I can fully second and support that statement with actual performance..........

Other than that, every original boat I've owned, and there's satellite pics on here to prove this, came originally with a 750 vac sec'y carb. Probably for warranty reasons, but one quick way to warm them up is an 850 CFM minimum with no other changes. No matter 454, 455 or 460. Just my experience to get a few RPM's and actually fuel economy out of them.
Throw a solid build on the engine with a good cam, I ran twin 750's with no problems. The thing with tunnel rams is almost as, and somewhat more complex, than running a blower. The sheer volume inside the tunnel ram intake is a vacuum nightmare, IMO, with a single carb. I don't care if it's vac secondary or mechanical, vacuum is vital with either. the slightest vacuum leak is detrimental. Now, with NO vacuum leaks, either carb is equal, in my experience, Mechanical or Vacuum.
With a single carb tunnel ram, provided the build is solid, and the cam is there to support it, personally, I'd be running an 1150 dominator on it, or at minimum a 950...........
Ray