castrada
I fitted my Hans over last winter, it's a bit more involved than you'd like.
You have to book yourself in at Arch (who I believe are the only accredited Hans fitters for 7's), attend with your car, cage off and seat in.
You'll then be measured up and the new belt anchors brazed in while you wait. This is to ensure correct angles for belts over the Hans.
The service from Arch was 1st class and a pleasure to watch a craftsman at work , but it was still a day off work for me.
Seat wise, I've got a Caterham low back race seat, I couldn't get on with a Tillett with helmet and Hans on, despite front spacers to get tilted back more. Your neck still gets flexed forward and I'm not the only person to pull their Tillets out as a result
Hope thats helpful
jerry