Hi GreenHornet. Sounds like a very interesting build you have going on there and no doubt with all your in-depth research it should be a winner.
I've not done any cd testing on the Centurion. I did a few things a bit different than the original plans called for such as windshield rake, overall height, ground effects, etc..
The original Centurion reported 128mpg@35mph.
Lane Motor Museum reports their Centurion at 45mpg. They must have a dragging brake, deployed parachute or something.
Both cars use the 750cc Kubota triple.
Both cars use a power robbing Spitfire overdrive unit too.
My Centurion has the optional Police Interceptor 850cc Kubota and a straight 4 speed. (The 950cc Kubota may have been reserved exclusively for the station wagon Centurions - citation needed!). For 2 summers now I easily pass 1000 miles on the 10 gallon tank and the only time I drive 35mph is in such posted speed zones. We have no freeways here in my vicinity and the roads are not exactly great, so the top speed of 65mph@3050rpm is perfect. I've even incorporated some styling elements which do nothing for efficiency but are "eye candy". One of the most notable is the Carroll Shelby Scorpion wheels once belonging to the original Centurion.
I've put all work on hold for now with the Centurion mainly because I'm knee-deep in a Tri-Magnum build. For this, I've hashed out similar views as yours regarding a hybrid or pure ev, but lithium isn't quite there yet - at least not the affordable stuff. As a premier lithium battery producer, A123 showed promise but has since gone bankrupt. Unless economies everywhere get better, the only lithium market they can currently support appears to be going to cell phones and the like - not evs...
RQ Riley has updated the Tri-Magnum as a diesel-hybrid dubbed the XR-3. I have my own human/hybrid ev reverse trike dubbed "The Aurora Project
" At 110 lbs it does pretty good and has some features most cars don't.
Keep up the good work - I can't wait to see what you end up with!