Here is a link to a blog where a fellow has done a very nice job of installings Groco IBVF flanges and valves: Far Reach Voyages.Com
Go to the Groco website: www.groco.net
Click on "Products" then "Seacocks and Ball Valves" then click on the picture of the IBVF. This will show you the sizes available.
We are just bringing in the IBVF. It looks like the IBVF-750 (3/4") will sell for $24.95 and the IBVF-1500 (1-1/2") will sell for $39.95. These are the two sizes commonly used for a toilet installation