Depends a bit on which model 2a (i.e. 88/109, diesel, petrol, ute, hardtop, wagon etc), and what sort of driving is involved - city, country, towing etc. 
In my view, the major drawbacks of the 2a for city driving, for example, is the lack of power steering, and in the 109, the turning circle. Power steering can be fitted, but I would think carefully whether it is worth the effort and cost, although not much you can do about the turning circle except avoid using wide tyres. Probably fitting power assisted brakes would help, as well, and this would be easier and cheaper.
For highway driving, first item would be some soundproofing! Next I would be fitting the anti-burst door locks and high seat backs from late Series 3.
Regardless of the type of driving, unless you are in the tropics, an early modification would be a heater/demister. Two speed wipers off a Series 3 might be worth considering. I would fit reversing lights as well, aand probably hazard lights.
John
				
			 
			
		 
			
				
			
			
				John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
			
			
		 
	
Bookmarks