Ronnie
I will check out the dimensions next time I'm down the garage - from meory the inlet pipe is 2 5/8" OD and connected by a 4 bolt flange. There are some more pics here -
http://www.haynes.co.uk/forums/showthread.php?t=4119 The can itself came from good old Ebay.
With regard to exhaust configuration it really depends on what you want. The different arrangements do not give you any more power - they just move the power and torque up and down the curves. Generally the longer the pipes, the lower down the curve the peaks will be. If your not familiar with the theory, it is basically that wherever you have a change in volume you will get a wave reflected. If you time this wave to be in sync with the exhaust port open you will create a negative pressure and actually suck exhaust gas out of the cylinder (giving you more space for fresh charge on the next intake cycle). If you look up helmholtz or organ pipe theory, you should be able to calculate for your engine for a certain RPM how long your exhaust runners should be. If you need any help let me know and I could probably dig the calcs out - good excuse for a spreadsheet!
For my own car, which will be mainly for the road, I plan to use a 4-1 and the longest primary runners I can package tidily as I would prefer a good low/mid range power than the max HP somewhere up the top of the rev range.
Out of interest Ronnie are you planning to weld up your own exhaust? I'm going to have a go at doing my own from scratch in stainless. Seems like a good challenge and one of those jobs that will probably be a complete pain in the a** but a satisfying one. Most bits seems reasonably easy to get hold of - the only thing that amazes me is the price of weld on merge collectors - yet to find any below about £55
