Unless your trying to squeese ever last HP out of that engine, I wouldn't bother with a cross over. Just from what I have read here, and what my frineds have gone through. Some problems have been water presure drop, and low engine temp issues, causeing the engine to run too cool at idel.
I have had one buddy gain a little bit on his top speed. Like 1 or1/2 a mph . But see the problems above.