Tom,
When I installed my A/C into my car, that was not so equipped, I took advantage of updating all that I could. As far as the condensor, the original can be used, however it is far from optimal for R134a because of the properties of R134a and the physical limitations regarding to size. To increase the surface area of the condensor a parallel flow design is best. Also changed all the hoses to a barrier hose with "o" ring fittings where possible as they tend to leak less than the barb type push on fitting secured with a hose clamp. The rec/drier is nothing exotic other than being designed to operate with R134a, uses a specific dessicant and available at any parts store. I also replaced the expansion valve. The system works quite well on all but the days the car (1800ES) sits out in the sun all day. With all the glass area it takes a bit longer for the A/C to pull the temp down inside the car, but after 5-10 minutes it is comfortable, at least where I am sitting. Hope this is of some assistance.

Earl
72 1800ES
74 BMW 2002Lux
02 BMW M Roadster