If you buy wisely and maintain it well - it'll be reliable as a hammer - i.e. very
There are always exceptions to this rule however and whatever we do, sometimes just things conspire against us and we can have unforseen breakdowns - however, they're simple, strong, effective workhorses and will even function when abused!
A good Dolly should be able to beat the 306 for reliability or at least match it, with ease!
I'd be looking at an automatic or 4 speed overdrive 1850HL - Returns good MPG and the ability to cruise in comfort on the motorway whilst having a nice slant 4 beat and a strong lump, provided you keep an eye on the coolant and make sure it's at the correct level every now and then
There are some very simple things you can do to improve reliability too - like making sure everything is in good working order, fitting one of Jod's aftermarket ignition kits, decent leads, plugs, coil, cleaning up the carbs, a decent fuel filter, a thermostatic oil cooler and so on