Three words: lithium, lithium, lithium.
I have 1320# of PbA in my pickup ('94 Toyota i.e. it's small) and it's a pig going up hills. I figure I could get better performance with about 400# of Thunderskys. Lead's gone up in price and lithium has come down. $1.10/AH is the best price I know of now (
http://www.evcomponents.com/SearchResults.asp?Cat=28).
Imagine taking 900# out of any vehicle...
Great project BTW. Here's a couple of links that may be helpful.
Russ Reiss' 1974 Chevrolet Corvete
Michael Shoop's 1987 Chevrolet Corvette