What tools do you have? Torque wrenches, feeler gauges etc?
Most head work will comprise of porting, chamber work, cam and valve train. On a stockish engine it'll give you a big upgrade initially, high hp is a different level.
I'm no expert but have attempted a few engine rebuilds and a gearbox rebuild due to a low budget. With the help of some knowledgeable people, my brother and the forum it has saved me a heap. I've learned a lot in the process.
I'd say have a go yourself, some fellow Sydneysiders might be able to help and if it all ends up being too hard send it off to be finished.
Have another chat to James and explain your choices, if you spend the money with him he may go the extra mile with you and help you out with other tips/info.
Peter Mac did this with me, he went way above and beyond what I expected. I'd suggest talking to him as well!