I built my car using a Tuttle plan and the SFI book, and it worked out well for me, the plan gave me working dimensions for a "average" size driver and the SFI book let me know how much I could deviate from the plan if I felt the need too. Also I was confident there would be no problem when it came time to tag the chassis. Getting the relationship of the seat to the rear end housing as ideal as possible to make the car comfortable seemed to be the biggest challenge, the rest was easy. Use an alignment bar, and do one final alignment after the chassis is completely welded and then last drill and ream the rear end mounting holes out to the bolt shank size. I also tapered the rear end mount plates in at the bottom 1/8 per side to make sure the housing will still go in and come back out, as things may move around a bit during the final weld up.