I did this whole think in 2008 when I bought my 1969 Series 2a ECR rebuild which had a pickup cab and a soft top and front roll bar with diagonal braces to the back with angled braces through the wheel wells to the frame front seat/shoulder mounts and came with a forward facing rear seat just laying in the bed loose. I got a full hard top which wouldn’t fit over the ECR roll bar. So I took it off.
I had a four post square box roll bar made from 2” sch. 40 steel pipe with four 90 degree elbows and four tees that mounted to the angled braces to the frame. This all fitted inside of the hardtop and had flat triangular gusset plates with holes in them welded into the pipes for stiffening and for seat/shoulder belt mounting.
I had the front facing rear seat mounted in the bed with bolts to the frame with the seat shoulder belts mounted to the roll bar and floor.
It all works great but it’s a pain to get into the rear seat in which you have to climb in over the top of the rear seat or the front seats and under the roll bar without hitting your head. So the final use of it is not optimal.
PM me for photos and more info.
Jeff Pearl
1969 SIIa 88 ECR Coil Spring Conversion
North Central AZ