On the subject of mpg, if the '76 under consideration has the 4.0 litre petrol engine, if you have reliable long term autogas supplies convenient for you then there's plenty of room underneath for an LPG tank or two.
Not sure on how young or old you are considering, but assuming its to be used in the UK isn't there a serious problem getting such a vehicle under 10 years old certified for registration in the UK, or am i talking out me backside as usual.
As for interiors, yes the 76 is old fashioned simple and practicle, apart from the plastic moulding across the steel painted dash panel the pics i've seen of 76 interiors look little changed from my '93 regd 70 series, and none the worse for that.
Insurance wise, presumably it'll be a grey import so in the hands of specialist insurers, VED wise as a grey better than a UK regd vehicle...so far...but anyone's guess what our elected dicatators have planned for us plebs.