Are you going to trailer it to events or drive it? Driving both engines is easy when racing but the heavy throttle, clutch and gear change gets a bit much when your working through traffic...let alone the heat and noise from the rear engine (+ MPG). Are you going to section the rear engine off with a vertical partition or leave it open?
A propper project, i havent seen one of these in a while well apart from the twin v6 lupo on Ed38 but the forums been down for ever
looks like you dont hang about,nice project,which reminds me theres a twin 20vt mk1 somewere near completion near Thirsk that ive got to go see