www.classicinlines.com has better customer service than clifford does. as for what you can do to gain power, since you are rebuilding;
1: .030 is about all you want to go when overboring.
2: use a cam that works in the rpm range that you plan on driving in most of the time. classic inlines has a good selection of clay smith ground cams, and if you dont see one you like, they will have clay smith custom grind a cam for you at no extra cost.
3: if you plan on keeping the stock head, mill it .050 to raise compression, .070 if you use a composite head gasket. you can then add, via an adaptor, a 5200 holley webber carb. or you can have the head modified to use a holley 2300 or autolite 2100 carb in a direct bolt on fashion. or you can add an offenhauser 3x1bbl carb settup.
4: if you plan on replacing the head, classic inlines should be able to get you either an aussie 250 2v head and intake, or an argentine head with intake and exhaust manifold at a reasonable price. however if you wait on the head for a couple of months while production ramps up, you can get a
NEW aluminum head from classic inlines(price yet to be determined) along with your choice of intakes(mike has plans for 5 different intakes that can be ordered). this head will bolt right onto you stock block with NO modification.
5: classic inlines also has three different brands of headers you can order, his own brand, pacemaker from australia, and hooker headers.
6: as usual a decent exhaust system needs to be installed, single or dual it doesnt matter.
7: if you want some real power, add a turbo. one of the guys on the fordsix forums has one on an early falcon, and that car runs in the low 12's to high 11 second bracket, with a 200 ci six! he is planning on installing one of the new aluminum heads as soon as they are available, and then he should be heading for the low 11 second bracket.
with the right mods you make enough power to surprise many V8's and ricers. dont let people tell you that a six cant make power.