I guess Citri-Strip is some rugged stuff. Is it safe to use on a walnut stock that has had the action bedded with Brownells Acra Glas Gel?

I'd test it on an inconspicuous spot first. Acraglas is a type of plastic. If no joy, get a set of English wood scrapers off Ebay and scrape it off. That's what we have to do on those two-part finishes.