Also note that good headwork will pay for itself if you're doing a fairly decent mileage in the car. When I first had mine done, my fuel consumption decreased by about 5mpg. Because I was doing 25-30k a year, the cost of the headwork was recovered in a couple of years
Something that is definitely worth doing is port-matching the exhaust ports in the head with the exhaust manifold - as standard there's a considerable step which can't be doing any good for gas flow. You can also knife-edge the collector in the manifold
However - I'f you're trying a bit of DIY porting, be extremely careful - headwork is all about flow - you'd think that opening up a port will flow more gas (be it intake or exhaust) but if you're not careful, you can create vortices (called laminar separation IIRC) through too-tight radii and you can also slow down the gas speed which can play havoc with turbine speed.
If I had my time again (and a fair bit more cash than I spent originally), I'd be giving a cylinder head to Guy Croft. He's already spent some time on a 5-pot Coupe head and of course he's done countless twin-cam four-pot heads (including Begbie's). IIRC, he had quite a few positive comments on the 20VT head, but he still found significant improvements.