Are the parking brake cables supported in some way as they leave the firewall
on their way to each respective rear caliper?

It looks like the passenger cable has a couple of tabs on the back firewall that are used, but after that is there a strap for spanning the distance from the firewall to the caliper?
Same with the driver side?
Where is the strap attached on the chassis?
And how long is it?

Any pics would be very useful of this area.
Thanks!

914-6's used 911 straps to hold cable. Might have been used on early -4 too but not shown in PET (38). Different numbers for different length. The rear control arm has a tab sticking up where they mount.

999.706.005.80
911.424.341.02
911.424.341.94