Replacing a Stag headgasket

[Skyedriver]

There's a car available at the moment, looks nice but has suspected HGF.
Now I've done a few Fords and BMC A series along with Hillman Imp alloy heads but not a Stag.

So having read a few things on Google, are they really that difficult to get apart?
What's this about the head bolts having slotted heads not Hex heads, how do you torque them up (or get them apart).

Not knowing which head it is I guess it's both need doing, and both heads skimmed to balance up?

What's the likely all in cost, both DIY and at a specialist?

Thanks all (prospective Stag owner)

[Skyedriver]

Well that was short lived, seems the car is no longer for sale......thanks for looking anyway.