Seats and Belts

I've recently acquired a 1970 IIA which has some after market front seats in. What I'd like to do is fit the standard 3 seats to the front but, include 3 inertia 3 point seatbelts at the same time. Has anyone here converted from lap / fixed belts to inertia before, and if so any advice? I was thinking of getting the center rear seat from a Disco which has the belt attached to the seat... would this fit?

I also want to either retro-fit forward facing defender seats in the back, or fit the side facing ones like found in the Country - again all with inertia 3 point belts... any advice welcome.

Here's a pic of my new purchase:

You'd need to look into it carefully. The seatbox is strong in the points where the belt anchor points are but not really elsewhere. I'd hate to have a crash and be sent through the windscreen with a chair attached to me....

I got a 3-point belt for the centre seat. The two points for the lap are on the official seat belt mounting points and the over-shoulder is to a decent sized spreader plate on the bulkhead behind the seats (fine for a SWB not sure how it would go in a LWB though, I think you do it to the floor somehow)

Got mine from Brookwells.. (search for EXT001-9) I think they do similar kits for the driver/passenger but I stuck with 4 point harnesses for these as it gives me and excuse to play with the missus tits after my skinny mate has tightened them up!

Driver and passenger seats are easy - drill the rear bulkhead near to the doors and fit the inertia reels (the original belt fittings are on here anyway). You'll then need the brackets that fit the sides near the top of the door and the bottom rail at the bottom of the seat base, readily available.