WTH... geez its a small oil leak and he wants to machine his engine head and cover???
To add fuel to the fire:
Need to fix a leak? You've got choices!
1. Thicker gasket or use a sealent
2. Increase the pressure the bolts are applying to the cover (more torque)
3. Flatter surfaces
Firstly, the cover and the heads are already machined, the casting is pretty much irrelvant for this discussion. I was chatting with a friend of mine who used to be a mechanic for 20 years and I was complaining that I absolutely hate fixing leaky transmission pans on my vehicles how even after following the procedures absolutely perfectly i'd still get some of them leaking after. He said "did you check the pan with a straight edge and correct it?" ...huh?
Yeah, the covers can and will warp, he would check them on a straight edge, and with a rubber mallet fix the pan before reinstalling it with a new gasket (and gasket maker if he wasn't confident with the pan), never had a customer come back.
#2, if you increase the torque on the bolts too much you WILL pull the threads out, so don't do it... if you really must do it, save yourself the headaches, drill, retap and use Heli-Coil inserts (with locktite on the coils), they can withstand several times more torque than the aluminium threads.