Here's my two cents: My first car was a 1965 Mustang Fastback that I bought used in 1980 when I turned 16.
My father owned and drove a VW 411, and my mom drove a VW Bug then. Our family later switched to Honda's, but also owned a 68 bug as a daily driver with a 2110 stroked motor that I built myself. In 1999 I decided to buy a new BMW 323is 2dr Coupe, I always loved German cars, and wanted to own a BMW at least once in my life.
Out of high school I went to work for a performance Automotive retail chain, called Supershops, and have sold many speed parts in the seven year period I worked in Auto Parts and Tire and Wheel sales. I left due to low wages, and wanting a better life. I sold conversion kits for a Chevy 350 in a Datsun 240z-280z by Scarab, and kits for a putting a Chevy V8 in a Jaguar. Would I do this in a BMW, absolutely not. Can it be done, I am sure you can modify the engine bay, motor mount brackets, and transmission cross member and drive shaft to swap it in, but it's probably not going to be street legal in most states, and you'll probably blow out the IRS axle and pinions now and then if you drive it hard. In California, cars no longer need smog tests after 30 years.
I love my six cylinder BMW, it has good torque, and power, and good gas mileage for a six. If you want more power, buy a 540 BMW, and add a Turbo charger to it. So unless you got money to burn, and have welding and fabrication skills and or just want a BMW that's out of the ordinary, keep the BMW as is and and buy a early Camero, Covette, Chevelle, etc, but remember that you'll get about 10 miles to the gallon around town, with that 4 barrel carb, and they aren't as comfortable to drive or work in every day. I would say that the new Corvettes are pretty awesome, and the new 2012 Shelby GT500 new Mustang with 750 horsepower would be fun to drive and own.
Jose F. Medeiros
San Jose, California
Thomas A. Edison: 'I have not failed. I've just found 10000 ways that won't work."