seat belt question for autocrossing with OE 3-point belt

Question for Tom Suddard:

EDIT: you can ignore this post if you answer in my other thread

is a harness with the shoulder belts joined in a Y considered a 5-point for the Challenge?

AngryCorvair (Forum Supporter) said:

In reply to wvumtnbkr and jfryjfry :

my current vision is to run a harness bar connecting the bottoms of the C pillars, just a hair lower than the bottom edge of rear glass.  it would be above the permanent part of the engine box.  just need to know whether or not standard shoulder belts will be long enough to reach that far back.

belts stretch, up to about 10%.  When we have to make long runs for shoulders in cars we crash, (which is often) I will use chain to elongate.  It won't break and it won't stretch.  
 

might be an option?  Or a properly built cable?? (Which might be quieter when not in use)

AngryCorvair (Forum Supporter) said:

I like the way you're thinking, and that would work if the engine box was permanent like in a typical mid-engine car.

MonZora engine box / firewall is disassemble-able for engine service, so I am loathe to add permanent elements which would interfere with that.

also, there are no strut towers in Corvair body. Rear suspension is SLA, with transverse leaf below LCAs, and dampers attach to chassis behind UCAs. Base of C pillar is main node of Corvair rear unibody, as that is closest to where Corvair spring loads react into structure.

I will figure out an elegant way to react / distribute forward forces of shoulder belts into the rear bulkhead.

Never said it had to be permanent.  Quite the opposite, in my mind.  I was imagining something similar to a front strut-tower brace that is removable for service.

I didn't anticipate the lack of strut towers, though.  But if the firewall is the best structure, then have the vee start in the far back corners and cross over the engine to the center of the harness bar.  Mount your harness and your 3-point retractor all to the cross-bar.