I'm one of the recruits, I asked what you meant by HUD because I wasn't sure exactly what you were looking for...a unit on inside/outside, some sort of visor...

Currently you can have rear facing video, OR MPH. They are however asking for input from us recruits on what else to allow, I don't think an RPM app will be worth it for them since it's really for skydiving, skiing, etc...but maybe a MPH over video feature.

What I really like about it, is you can create maps with elevation and such of the rides you do. Plus a lot of other cool recordings.

To get it set up with a rear facing camera it would cost about $550.

Shop for MOD Live GPS Heads Up Display | Recon Instruments

You would have to get the LIVE version, also if you have an android phone, you can link that to the device.