I've just done this in ours. There were holes already existing in the engine lid (which had bolts through it that I had to remove) which I assume are there on all commers, and the seat which is an original had bolts coming down off the frame that slotted through perfectly.
It was a lot more simple than I expected. I also fitted a lap belt using the existing mounts for the stalks to the driver and passenger seats.
I put a non original seat in my last van .....well. what I mean is, it was a commer seat but not a specific middle seat....it was simple enough, just a matter of removing the cover and sponge and drilling a few holes, only thing is, it sat a tad higher than a specific middle seat but worked just fine....I could still lift it to access the engine bay
Panky Thanks, Can you believe I found one my brother picked it up from sunny Wales only yesterday, It may be better than mine but I dont want to be greedy.
So go get it people they are hard to find I had been trying almost a year.