Add a diverter?

[Bob Rooks]

Cross tells me I need a conversion plug and can then tap the byd port with a 3/4 16 SAE-8 fitting.

There ya go! Now all you need is a dual action (DA) valve and some hose and fittings (and of course, your grapple). Surplus Center is a good source for valves and fittings -
Hydraulics | www.surpluscenter.com

You will also need to install a relief valve in the new grapple circuit to prevent damage to the grapple and/or the bucket.

Usually a good NAPA store has fittings and can make up hoses for you.