The stock condenser is fine, I recommend you stay with it. It is possible to convert to a parallel condenser, but you are looking at a whole bunch of custom work to do so. A generic parallel condenser won't use the stock mounting points, so you would have to fabricate the mounting. Also, the inlet & outlet fittings are in different locations (and likely different sizes) so you need to have custom hoses made up. It can be done, but it's a bit of money and a bunch of time and effort.

Given that you reside in the great white north, I'm going against the grain and recommending a conversion to R-134a. It's just not going to be worth the hassle to trek over the U.S. every time you need a/c service or a refrigerant top up. When correctly converted, R-134a works better than expected in these cars. I ran it for a while in my 1987 wagon - in Dallas, in July. It was surprisingly adequate. The key is to insure the entire system is up to par. Replacing the condenser is a good start. Another important step is to insure that your recirculating air door works - the a/c is much cooler when recirculating air through the car than when sucking in hot, humid outside air.

Replace the expansion valve and associated o-rings. It's a known leaky point on these cars. Need to do the one on my spouses 1993 300E, actually. You'll need to pull the exp. valve to flush the evaporator prior to conversion anyways, so there's no extra labor required.

My $.02,

- JimY