Should work fine. I'd play around with the ratios, it'll be confusing because the directions on the can require you to change the ratios for Awlgrip. Mix Interthane 990 as normal, then add flattening paste, then reduce as required. If you are roll applying instead of spraying, viscosity is much less of a concern. If you are spraying use a Zahn cup to reduce to the correct viscosity. A cheap
#2 Ford cup will work, no need to get a nice expensive one. Do a couple of test runs on something disposable first.