A few days ago I look at the data sheet for Great Western wheat malt an the DP was 180. I think Briess is 160. Wheat can easily convert 75% adjunct...but then crystal is already converted anyway.
Sorry for a stupid question, but can you explain what this means please
This information is about enzymes and how they would convert the starch in adjuncts to sugar. It's probably not necessary for a new extract brewer.
Take the original recipe and reduce the whole thing from 6 finished gallons to 5 to fit your gear. This is just a simple percentage for both the grain and the hops. 5/6 = 83% Buy an appropriate amount of light malt extract for the main part of the malt bill (the 2 row pale malt). It's been a while since I've made an extract beer, but this should make up most of the original gravity, which ought to be about 1.065. I'm thinking about 9 pounds of extract would do it. Steep the crushed wheat, munich and crystal at about 150-155 degrees for 30 minutes or so in the water you are going to be boiling the batch. Remove the grains, add the extract and bring it to a boil.
Follow the hop schedule, but use about 80% of their recipe.
I hope I haven't oversimplified it. I'm sure if you hit the approximate gravity and have the appropriate hops it'll turn out similar to the IPA you want.