A 1986 2.5 petrol will be a thirsty ***** I tell you, but a good reliable runner non the less. I have a 1986 2.5 diesel 90 (they're not called defenders at that age) which is a very good steady (slow) runner. Just make sure that you drive as economically as you can - it is technically a tractor. The petrol engine is a bit quicker but just as solid a lump as the diesel. I don't know how easy a job the bulk head is, but I think it involves cutting out the corners and welding new ones in. Probably just as easy but replace the whole thing if it's that bad.
*depending on how you drive it, but still reasonably thirsty anyhow
-Pos