As i mentioned, i tried to adhere to the IVA specs even thought i strictly didn't have to, as I'd never built a car before and i was quite enjoying learning news things and new skills. Or in the words of my wife, "playing about!"
As i've gone for retractable belts my setup is a bit different to Pauls, but you could easily chop-n-choose bits of both depending on how you want to do things. i.e. the top plates that Paul has done, i could have used also if i'd thought of doing it that way at the time!
I used the existing seat belt mount point on the chassis for the bottom of my belts (shown hanging loose in the below photo) and then welded a threaded tube onto each side of the body frame to mount the release stalk on to.
The release stalks are shown bolted in place in the below pic using the original seat belt bolts from the MR2 donor.
Those were seam welded in place all along both sides and are very strong and i believe have passed IVA on some 7 replicas. Although others have added an extra plate over the top in a similar vein to Pauls corner pieces for extra peace of mind if they are doing more racing.
I then welded the top mounts onto the top of the frame (again, seam welded all around) for the belt guides to bolt in to and then two more threaded tubes were welded onto an additional sub-frame i added between the cockpit and the fuel tank to hold the bottom of the retractor mechanisms with some brackets i made up.
On the below photo you can also see that the space between the Sammio frame and my additional seat belt frame has a plate welded across it for the handbrake bracket to bolt to.
And yes... I did get a bit carried away playing with my welder!