If a 1.75 ratio rocker arm is going to give you 0.575" lift at the valve, then a 1.70 rocker arm will give you about 0.568" lift....or only a measley .008" less, give or take. In your combo, this won't be seen on the dyno and you certainly won't feel it in the seat of your pants in a jet boat. So look for some dime-a-dozen BBC 1.70 ratio rockers.
If you want to spend the money, the Crane Golds seem to be the industry standard...about $335 from Summit Racing by the time they are in your hands. OR, it just so happens that you can get the Millers in a blowout sale for a mere $175/set from:
www.adperformance.com/Ask for Brian and tell hime Paul Kane sent you for the Miller 1.7 ratio rockers for $175/set. (The Millers are made of 7075-T7 aircraft aluminum and have chromoly polylocks)
LO
p.s.: Jim, I suggest you jump on that deal too; Jim Miller just claimed my last set of 1.7's that you inquired about and I sure as hell wouldn't sell 'em for that cheap anyway.

p.p.s.: maddog20, if you don't understand propelry esablishing rocker arm geometry with a custom valve train, then get the help of somebody that knows what they are doing.