How lovely that you're giving your old boy a new friend. I'm so sorry his previous companion died recently.
What I have done when bonding is, when they're at the point that they're getting along well in the neutral space, I move their bonding pen into their permanent space and move the bunnies to the new location in a carrier. Then, usually, they have a bit of a setback as they decide who's boss again in the new space. Once they've settled, I increased the size of the pen, and keep increasing their space every few days until they eventually they have access to the whole room/space.
Edit: Since he's not used to being handled, could you lure him into the carrier with some food?