If you look into the stock head, there is casting and machined sharp edges just inside of all the runners.
This creates turbulence, and that lowers the ability to make power in some cases. (Some swirl is good for mixtures at lower engine speed, but pretty much, it lowers the power ability of the engine in most cases.)
Ok, so if you are not changing to larger valves, you can carefully clean up the runners where they come into the valve seats. (Smooth and remove all high, sharp edges, and do not nick the valve seats! A few layers of blue masking tape over the seats is good insurance.)
My setup has 1mm larger valves, and then I ported the runners to smooth them into the now larger valve opening. (We cut the seats down slightly, and the 3 angle job smooths flow over the now larger seat opening as the valves open up.)
On the intake side, just remove any large casting flash, but don't waste your time here. They are plenty large for this engine.
On the exhaust side, there are gains to be had if you port the runners larger, but not TOO large.
Do not gasket match, or port match the exhaust side of the head. I left about a 1mm to .5 mm "lip" where the exhaust gas spills into the header. Then I also opened up the header to make the "lip" even larger, closer to what they did stock. (The lip keeps some exhaust flow from reversing back up into the head, this boosts low/mid range tourqe on this engine, but does not cause so much of a flow restriction, that it will not pull to redline if your turbo is sized correctly.)
On the combustion chamber, drop in some old valves to protect the seats, and then blend/smooth all sharp edges in your chamber. I layered blue tape everywhere I did not want any carbide bit marks to end up. (Like where the head gasket seals up...) Don't go hog wild here. The idea is to remove any sharp edges that can cause problems if you run lean, and smooth the area where flow can be disturbed by sharp edges and breaks near the valves.
My head is also thermal barrier coated on the combustion chambers, exhaust runners, and intake runners have thermal dispersant along with the rest of the head to keep everything as cool as possible.
Whatever you do, replace your old worn out stock valve springs with new ones from Comp Cams. (They are originally made for a Big Chevy V8, but work great in our engines, and they are CHEAP!) About 60.00 and shipping for all 24 of them. Do a quick search, and you can find the part number, and order them direct from Comp Cams.
Good luck.
PS. If you ever do any port work, buy a carbide bit with the larger cuts in it, and use WD40 to lubricate the cutter from time to time. It makes it messy, but it cuts way better with lube, and it will not clog up your carbide this way. (You can remove quite a bit of material quickly with the large cutter and WD40, so start off slow, and make sure you don't break into any coolant passages. There is quite a bit of material in most places I've noted, so do those, and leave it alone..)
