Does it just smoke on idle?? Or does it chuff smoke out when the engine is under load?
My Valver did somthing simlar, no smoke while driving, but leave it a few mins on tickover & it chuffed smoke out. Everyone told me stem seals, when in fact it was the valve guides that were fooked. On valvers of that age its fairly comon, the guides become worn with age & become oval. So when you drive it hard not much oil can get past the valves, but on idle the oil seeps down the guide into the cylinder. It cost me 1200 notes(tsr prices) for new valves, guides, new head, tappets, stem seals & a few other bits & bobs.
On the other hand if it only chuffs blue smoke out when you boot it, then its your piston rings & or worn bores

Even more pricey i'm afraid. But at that milage i'd guess its guides or stemies.