Gas Cap Replaces Briggs & Stratton 596250

I have a 21" Murray Lawnmower that I bought at Walmart. It uses a Briggs & Stratton 450e engine on it. Every time I mow around the lilac bushes the cap got spun off. Normally I'd catch it and fix it but one day I didn't notice until I ran over it on a subsequent pass, destroying the thing. This engine uses two different style gas tanks and thus, two different gas caps that are NOT interchangeable. The style I have is the newer, but rarer style. After ordering a replacement from B&S and wa