If it's got AL clutches and wiring and modules on it, I'd just get the AL monitor like you were thinking. Integra (used) would do it, or new Incommand if you want nicer/current setup for more $$. I'd think you could feed it the GPS from your Trimble but that's about where my experience stops. Been around plenty of AL monitors and surevac planters but not w/ trimble GPS. 

You'd need at least ag leader power harness and display cable as well to power the monitor and CAN system. Maybe another high current power from batteries to planter, see what connectors you have at the front of planter.