Some time ago I bought a second hand Asfir fuel tank guard and today got around to fitting it. The biggest problem was getting the old one off; rusty nuts seem to be my nemesis with the Jimny! Luckily, my Irwins bolt grippers have done the job and got them all off.
The old fuel tank guard was rotten and certainly not up to the job of protecting the fuel tank. The bolts holding the old guard on needed replacing. I used some 10.9 Hi-tensile steel bolts. The specification you need are M8, 25mm long thread and a thread pitch of 1.25mm.
Here is the new guard before fitment to the Jimny (the brown stripes are the parcel tape that I couldn't be bothered to clean off!).
Fitted to the Jimny.