In case it helps others, here are two messages I sent direct to Tony. When I wrote them, I had not seen his post on the forum and did not know he has a SV:
These fit the front. They could conceivably be fitted in the rear of a GT (no hood), but only if they were mounted in the boot area, with slots cut in the rear trim. When we had small daughters, I did fit some seat belts in the rear, but I doubt that the shoulder mounting would pass any normal strength test as it was cantilevered back from the wheelarch belt mounting. It's hard to fit more than lap belts in the rear unless you butcher the car as above.
(Tony replied that his next jobs are electric fan and elctronic ignition)
Electric fan is an excellent mod. Don't be afraid to remove the fan driven by the engine. I personally wouldn't bother with electronic ignition, but if I did fit one, it would have to get rid of the CB points.
I recall submitting quite a lot of detail about the Securon belts. Have you found it? There are two types, and with one of them, you have to remove what would in some cars be the 'fairleads' above the shoulder. Just cut the metal (avoiding damaging the belt!) , open up the slot and remove them. I presume your car is either a SV tourer or a SIII to V GT. If it's a SI to IV tourer, the reels will certainly make opening the hood stowage cover difficult. The answer could be to move the reels up and forward by means of metal straps bolted to the wheel arch mounts.