Personally I like a Pertronix unit in the stock recurved distributor, easily hidden and looks stock.  For a daily driver I think the Duraspark conversion is the way to go.  For all out performance MSD stepped up to the plate for us a few years ago with their unit and it has many of the same easy tuning features of the H.E.I.

When I was building my 460 about 10 years ago I ran across a few of the Davis H.E.I. units clearing on ebay for as little as $130.00  I went with a 429 CJ distributor and a Crane trigger with a Crane HI 6 box.  The H.E.I. just looks fugly in a Ford, especially the Flathead and I can't see that huge cap fitting in a '57 to '59 Ford without cutting the firewall seam and some serious massaging with ball-peen hammer.

I'd be a "NO SALE" on an H.E.I.  It's like switching to a one-wire alternator, sure the GM unit can be made to work, but so does an early '70s Ford alternator with a $25.00 compact solid state voltage regulator mounted to the back of it.  I just like to keep my Ford as Ford as possible.