Well, as you probably know, I successfully bonded Sammy and Roo as adults a few months ago.
To start with, we put them in separate enclosures (cages at night, outdoor runs during the day - it was September) side by side so they could get used to the sight, sound and smell of each other with no physical contact. During this time, there was a lot of interest/curiosity on both sides, but no signs of hostility.
After a week of this, I tried them on a lap together. They were both quite tense and sat a little apart. I had them out on a lap for an hour every evening for a week and by the end of the week they were relaxed and snuggling.
Then I tried introduction on neutral territory. They were fine for 45 mins then started getting a bit cross, so I decided they'd had enough for the first session. I tried them again a couple of hours later and they were fine, but then we had to go out so I separated them. After that, they were together every time anybody was available to keep an eye on them. They did a bit of mounting and a LOT of nose-to-nose stuff but no worse, and we were gradually able to reduce supervision until they were together full-time.
HTH!
P.S. Have you looked at the 'Barmy 4 Boars' website? That was where I learned how to try bonding our two!
P.P.S. - Just realised you asked about these boys before. You have sows as well, don't you? I'm not sure you will be able to get boars to live together peacefully if they can smell sows.