If you want to do an extract version, I believe Northern Brewer sells liquid rye extract and maris otter extract. So you can take the all grain weights and multiply by .75 to get a proper conversion of grain to LME.
I would do 5 lbs of maris otter LME and 1.6 lbs of rye LME to keep percentages and OG similar between the two recipes. Then keep everything else the same but remove the rice hulls. They're only there to prevent a stuck sparge, which isn't really much of an issue with only 20% rye anyway. If you leave them in there you just waste space, money, and wort.
Overall percentages will slightly change. But you can play with the weights a little in any recipe calculator. The idea would be to keep the percentages between the two recipes generally the same. I also imagine the roasted barley will be less helpful with an extract version, as it is there for color correction. Again, you can just put this in a recipe calculator and dial in the SRM, grain percentages etc, if you're concerned about precision.
Steep the grains for probably 20-30 minutes. Bring to boil. Take off burner. Add extract. Place back on burner and boil for 1 hour.
I've never used maris otter or rye extract. But the rye grain has such a great character, I'd reccommend doing a partial mash so you can get the rye goodness. It's a million times easier than you think. Its essentially doing a grain steep for 60 minutes instead of 20-30. You can just put some maris otter and rye with the specialty grains in a large bag and do it all on the stove (if your kettle is big enough).