Ad seems very light on info.. and pic's thats a shame. There was a chap racing about 15 years ago
who had a formula bantam 60's spec but with a Starmaker engine shoe horned into the frame..
Is it possible to make a 250 out of a bantam engine? And why if you intend to race aganist bantams?
However if it turned up in Britain it would need to lose some capacity and shed a couple of gears....