Hi m8,
You never said what your dad drives so I will guess its a v model, if it is both heads are best done at the same time, it will save a lot of work later. I would not use anything but VX/GM bits because the aftermarket gaskets and associated bits you will need do not fit, or as reliable as the true OEM bits. New head bolts are a must! The cam cover gaskets in particular will almost certainly leak after a while as will the exhaust manifold joints if you try to save a bit by using aftermarket parts.
Also you MUST use a torque wrench and torque everything by the book. The top end is alloy and plastic so is not tolerant of overtightening anything because it will end up stripping the threads.
You might as well do everything you can while you are on with the heads to prevent having to do the stripdown again for something you thought might be ok, the thermostat, the transfer pipe seals, and of course the transfer bridge seals at the back. Have a good looky at the HBV while you are able to get to it easily.
Either mark the mating ends of all of the connections and pipes, particularly the vacuum pipes or draw good diagrams. I take digital photos from every angle!
Finally, grow some spare new skin and patience and have a large swear box handy. You will probably need all of them

All your gasket sets and head bolts can be had from here;
http://stores.shop.ebay.co.uk/GASKETS-for-CLASSICS__W0QQ_armrsZ1the choice of aftermarket or genuine is yours because they sell both. Note that the difference in cost is not so big either!
Hope good fortune and weather are with you.
GudLuk