Is it a standard 20 or a lightweight? The 20s are a different situation than the 12 gauges, apparently because the 20 gauge carries a higher pressure longer in most loadings. I believe with the 12s the skeet barrels had the biggest ports (0.086") to function reliably with lighter loads, whereas the 'standard' 12 gauge ports were 0.079". I believe they also recommend not shooting anything heavier than 1-1/4 ounce (or it might even have been 1-1/8 ounce) field loads out of those guns.
On the standard 20s what I have shows a 0.076" ports for everything, and for a lightweight 20 a 0.067" port size for everything, but the 3" magnums, so with the 20 gauges it looks like you should be okay for any 2-3/4" 20 gauge loads. Shot size won't matter, especially with that open a choke.
A lot of people, me included, really like those skeet barrels. My LT20 was a quail harvesting machine with that barrel.