Is it possible to use anything smaller than a 1000cc bike engine? perhaps a 750?

Some of the first BECs used Fireblade engines, which are 900cc lumps. Much less than this and, unless the car is featherweight, the lack of gee gees will become an encumbrance, as there will be no torque to make up for the lack.
You could always use two 750s

there are some fokes like me,

that use a VFR800 engine (782cc)

the reason for me is simple, lower fuel consumption because i'm only 21 years old soow need to pay the fuel..

TKS

Unless you're building a single seater???
Pat...

Do a search, there's been several threads on here in the past discussing it at some length