I hate to see the need for rear seatbelts (lap belts) get in the way of buying a very nice early car, but all research so far suggests that while later cars have pre-corroded mountings already in place, the early cars don’t.
I assume of course it’s possible, but is it practical (taking the body off counts as impractical)?
Does anyone have any experience of doing this, having it done, or cunning top-tips?
Andy, you are correct in saying the later cars have pre-installed and CORRODED rear lap belt mounting plates.
You can fabricate and instal mounts on the earlier cars yourself.
Basically the seat belt are plates with a very small bent lip at each end (thus forming a channel). 4 small bolts (say M6 or 1/4UNF) are used to secure the inner and outer plates to each other. There is a captive nut welded to each of the plates fitted “outside” the passenger compartment which the belt anchor bolt screws into.
Access for the outer mounts is easy: they fit inside the inner wheel arch at the bottom just forward of the opening for the suspension I(plus a corresponding inner). I’ll take a photo later to explain if you give me a PM.
For the inner seatbelt mounts, these fit inside the vertical surface of the backbone section of the fibreglass, back into the corners of the rear seat cavities: you will need to get the car up on a hoist or similar to make fitting of this possible. However the chassis does not need to be removed.
Couple of tips. Use a stepped drill not a twist drill to achieve relatively neat holes in the fibreglass. SJS appear to list at least some of the parts off the shelf. They probably sell them in plated mild steel. However I decided to go for stainless, but this meant I had to fabricate instead of purchasing. Note that there is not a lot of clearance between tyres and the seat belt bolts. For this reason, I decided to use a low head bolt screwed in from the outside and a nut on the inside. Becauuse access is not to difficult for the outer belts, I decided to forgo the captive nuts in this case.