Jim Nordin asked how others have used the space where the header tank goes when it is not used.  I did not install the header tank at all but rather built a small bulkhead for the forward hinged canopy to drive off of.  The space up front was used for the battery as well as an avionics "shelf" above the passenger's feet where I installed MAP sensor, VM1000 computer, AOA computer, voltage regulator, etc.

See http://www.lancair.net/pix/olsen-construction/HPIM0099 for a photo of my firewall-aft area.

BTW, I cannot recommend strongly enough placing the battery up front for CG reasons as well as reducing the electrical losses that would have been incurred in long cable runs to the starter.  My CG is at the very front limits (the expanded limits from Lancair of a few years ago).  When Orin Riddell test flew my plane this summer his comments were that this was probably the nicest 320 he has flown in terms of pitch stability.  I do have the MKII tail.

Hope this is of help...

Dan Olsen
N320DK