plenty of overlap. you'd be slowing the intake charge unreasonably beyond certain (F1) engine speeds to the detriment of volumetric efficiency if you had no scavenging/overlap - flow inertia is simply too great.
you'll never get cam specs off a current engine design as you'd be a few calculations away from getting good estimates of valve size, inlet harmonics, port lengths, bore size, thus stroke size, etc... no way never. your best bet is to look up photos of 5 year old or so engine components that get sold off for memorabilia's sake and make a qualitative estimate on what the cam specs are from the photo.
i'd personally just build a 1-D gas dynamic model (some good freeware programs around for this) and play with the specs until you're there. the challenge then is deconstructing a mechanical solution that (a) works and (b) meets your dynamic aims for factors that affect the gas model.
e.g. know what you want your design to do then work on the solution.
that said there's a lot to consider in interactions between cam profile/effects and inlet/exhaust characteristics. far more variables in getting a working cam profile than what you'd pull of someone else's work, you'd need information on the whole picture to make it work decisively.
from your website jlcortex you seem to have an idea of what's involved... interestingly you're serious about building it. i have some small experience in high performance single cylinder engines... 18kRPM is very ambitious!
PS: this...
The advantages of a five valve head are that if you reduce the size of each valve, they can be lighter and therefore accelerate/decelerate quicker. Having 3 intake valves means you can have the same valve intake area but have lighter valves.
...is completely wrong.
