cylinder head casting numbers.

[rayofleamington]

thank you, at least I have a couple of heads if the worst happens, 3000 miles about 5 years

On that kind of mileage with UK fuel, I'd really not worry about needing an unleaded head!
If you want a bit more poke, I'd recommend a 12G940 as being the best bang per buck, as the 12G295 are pricey in comparison. The reason the 12G940 is cheaper is that they are fairly common but to fit to a 948/1098 block you'll need to make sure the valves are well sunk (it's fairly cheap to get the seats cut deeper, but adds to the price unless you can get somoeone to do it as a freebie)

[bmcecosse]

Exactly - but to use a 12G295 head it needs to be skimmed by 60 thou anyway - which costs far more than the valve seat sinking on the 940 head. The 940 is by far the better head - I have bought them for as little as £5 !! And it needs NO skimming on a 948 or 1098 engine. But you do need to use the 1275 gasket and rockers - and make some slight provision for the heater tap to make sure it doesn't wear a hole in the battery. A slightly different top hose will be needed too - this can be cut from a bottom hose.
YG refers to my comments re the 948 camshaft - just fitting a camshaft from a 1098 engine (AEA 630) will make a v worthwhile difference to a 948 engine - the MG cam is better still, but best used with a decent head and carb/manifold arrangement.