> So far I have done:  -water pipes (changed the rotting metal ones for
> the plastic ones) -heater matrix -new fuel tank (in place of rotting
> one) -engine oil flush & change -brakes (checked - seem ok) -cam belt
> (with help of a a mechanic friend), timing etc

Welcome to the list.  One blatant item is that you have not replaced is
the fuel lines.  Vanagain.com sells a kit with all of the pieces.  This is
important as the fuel lines are OLD and likely cracked with heat and
age and are under HIGH pressure.  Faulty fuel lines is the the #1
cause of engine box fires.  Do it sooner rather than later.  Malcolm