You would have to find a Getrag 245/11 OO BJ from an E30 323i Sport, or E21 323i Sport. A dogleg Getrag 245/11 OO BJ has similar gear ratios to the Getrag 250, and ZF 320/310. Found a link off Google.
http://www.bmwe21.net/?page_id=124The only reason I would put a Getrag 265 in an E30 is putting a high hp/torque engine in it. Like a m21, M51, M102, M106, S52 turbo, M6x, or M7x. North American spec 1982 528e with manual transmissions had Getrag 265 with a removable M20 bell housing.
It would be interesting to see a M60 powered E30 4 door still sporting 14 inch bottle caps ...
If I really would smash a €1000 on a gearbox it would be on a E30 M3 dogleg. But then again I would lack the 6th gear
, but that would be compensated with the sport feeling of the dogleg box.
You say that this dogleg box would fit? what bell house is required to fit a dogleg to a M42?