following should give you more information than you wanted to know about 6 cylinder versions of the E12. BMW never officially imported either model to the US, but some 323's were brought in by gray market importers and others were imported by individuals.

There were 2 basic versions - the 320/6 which had a 2 liter M20, Solex 4 bbl carb, single exhaust, rear drum brakes and most often either a 4 speed or automatic trans, and the 323 which had a 2.3 liter M20, Bosch K-jetronic injection, dual exhaust, rear disc brakes and most often either a 4 speed or 5 speed OD manual trans, although some were fitted with 5 speed CR transmissions.

If I remember correctly, all 6 cylinder E21's used the same 2 piston caliper/vented rotor front disc brakes installed on '77 only US-spec E21's and unique front struts which used different shock inserts than 4 cylinder / US spec units; disc brake rear trailing arms are a direct bolt on replacement for all drum brake cars and use the same rotors as disc brake E30s with E21 specific calipers. The same Volvo 240 Turbo caliper upgrade that works for '02s can be made to E21's if additional brake lines are added, and E30 rear calipers can be modified to work on E21 mounts.

In addition to the powertrain differences, euro E21's lack the front and rear frame reinforcements for the US spec bumper shocks, the rear valance is significantly different, and the many 323's that did not have ac installed have a different lower console than US spec cars.

More than a few 6 cylinder E21's (as well as some 4 cylinder cars) have had engine upgrades to later versions of the M20, as all M20 blocks are essentially the same as far as mounts and accessories go (except for distributors); an M20 install in a 4 cylinder E21 can be accomplished by installing the appropriate bolt-in M20 crossmember for the year of the car.
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Barry Allen
'69 Sunroof
'82 E21 (daily driver)
'82 633CSi (wife's driver)
'79 Datsun King Cab (yard & parts hauler)
'65 El Camino - for sale - anybody want a hot rod?