Middle seats and seat belts into panel van

Just bought what appears to be a reasonably priced Piaggio Porter to replace my dead (cam belt and body stating to rot) HiJet .

The Piaggio is a panel van and I naively hoped the mountings for seats and seat belts would be there unused and waiting for me to simply bolt them in...  

Assuming they are not there just needing to be drilled out:

1) What would easiest seat be to put in middle, individual ones on the square plate or the bench normally at back ?

2) What is best way to fit them ?  I assume self tapping bolt insufficient but would a bolt through the floor work ?  Bench would need a substitute for the clips on wheel arch in the window van.

3) Same re seat belt mounts - could I screw a plate with a mount on for the glides and rollers or should I get my friend who can weld to put plates with a bolt on ?

4) Are HiJet window doors and Porter panel doors interchangeable ?  Porter door look identical but has some two electric contacts sticking out.

Vans below - left the donor vehicle, right the new one.  Re funny plates, I am on Guernsey and 35 mph max speed limit and no need for adults to wear belts in back, they would be for the child seats.



Cheers and apologies if I am duplicating but could not find much re seats.