Nothing holds a marquee better than a real marquee retainer
Hi Craig,
First, nice work on your Defender/Stargate cab! Great work on your site and detailed info on building the cab.
I would disagree, though, that nothing holds a marquee better than a Happ retainer. Especially if you are going for a classic/retro look for your cab. Many, many classic cabs used metal angle retainers and they look very sharp and clean on a cab. Here are some pics cabs in my collection, all of which used the original metal angle retainers:
Williams

Atari

Gottlieb

Dynamo (generic)

Stern

My own MAME cab. I bought a length of 3/4" x 3/4" aluminum angle from Home Depot and painted it black. Cost: ~ $6

And here is a shot of a cab with a plastic Happ retainer that I snagged off eBay.

I'm not saying that the Happ retainer isn't any good, but I prefer the more traditional metal retainer look. IMHO, the plastic Happ retainer looks a little cheesy and aftermarket, but maybe I just like the looks of the classic cabs a little better...