I can't give much detailed information, but I'll give a quick rundown:
- drain the sump and cooling system.
- remove the carbs from the heads
- and the inlet manifolds too, if you want.
- There a 6 six 17mm bolts holding the heads onto the block. They are quite large. To access the top 3, you may need to remove the cam covers.
- Loosen all 6 bolts, bit by bit until they are all free. Be careful not to mistake the crank main bearing side brace bolts for head bolts!
- You won't be able to fully remove the bolts with the engine in car, but withdraw them far enough to pull the heads out.
- Clean the mounting surfaces on the head and block. Make them spotlessly clean. Brake cleaner is great for this, leaves no residue. Or use a kitchen scrubbing pad. NOT A METAL ONE!
- If the car ever overheated badly, like 100 degrees celsius, you may want to get the head surfaces 'skimmed'. A machine shop can do this.
-Put the new gasket in place.
-Put head in place
- Torque up 6 head bolts in the order given in the workshop manual.
That's a very brief rundown, I'm sure I've forgotten some things, but you can see it can be done.