conversion kits did exist for the fuel change. It was mostly about putting in harder valve seats. The lead was a useful lubricant for the valves.
My idea is that the small block Chevy engine is ubiquitous in the hot rodding world, and it is often combined with a Turbo350 transmission. This combo (or one roughly the same shape) has now been built by GM over 100,000,000 times. They hit that milestone in 2011! http://media.gm.com/media/us/en/gm/news.detail.html/content/...
So we take the Remy250 motor, used to propel the Chevy Tahoe Hybrid (I own one), the Remy is small, about the size of the torque converter in the Turbo350 transmission. That leaves the shape of the engine as a shape to fill with lithium batteries, and the rest of the transmission case can hold the inverter. There is enough room, I have measured.
You may only get 50-100 miles, but it could be a drop-in replacement. Since all the mess is self contained in one blob, it is a matter of yanking the old stuff out and shoving the new stuff in. Basic hot rodding, being done since the automobile was invented.
If it could retail for $20,000 to $25,000 the aftermarket industry would eat it up. I am a SEMA member for 12 years, so I know.
Any VC want to fund this idea? I have most of the pieces pulled together, just need to pay for some engineering time.