3-point seat belts

[GrampaTim]

I'm installing 3-point seat belts in my Lotus 7 replica, and need to have any input on how high the shoulder belt anchorage should be above the floor or seat. I'm seeing around 35 inches for production vehicles, so I need recommendations for putting a 1/2" bolt through 1 1/2" roll bar tubing without kinking, crushing, or weakening the roll bar integrity.

[Croc]

 

For reference, with the DOT 3 point belts in a Caterham , the shoulder anchorage was installed at the base of the roll bar on the chassis.  Photo below - ignore the race harness, the DOT belt is the one right next to the roll bar base and tonneau.  This may be high enough for a shoulder as that rear firewall part of the Caterham chassis frame is high enough relative to shoulder height once seated.  

 

 

 

 

 

If that positioning is ruled out in your car because it is not high enough, then back to your question of drilling the tube, I have always seen the hole sleeved with a metal spacer with the bolt running through the inside of the spacer so that it takes the compression weight rather than the hollow roll bar tube.