I need to replace the head on my 2.5 n/a 1985 110 s/w. As it's already done over 180k I think that now is the time to upgrade to 200/300 tdi. What should I go for (200 or 300) and do I want an engine out of a defender or a disco? Then there's exhaust, engine mountings. Will my gearbox be ok? Any...