Kazzo, how did you go with the itch?

I'm looking for tips to have a seamless introduction of a new horse to my old boy. It's been a long time since we've done it and he was younger and fitter. I'm concerned there will be an initial fight and my old boy will get hurt. I am able to separate them in different paddocks but want this to be short term as I want them in together. Is it as simple as having them hang out together for a while on lead ropes or doing a gradual paddock separation intro?

The new boy is much bigger and while he is very patient and quite a gentlemen, I know he'll only take so much from my grumpy old man.