Hi John,
I have not seen a Cal 20 with a Junk rig but my first experience sailing on Lake Michigan was on a co-worker's Cal 20 that he used for club racing. I like the no-nonsense raised deck on the Cal 20. It has a lot to offer for the LOA.
In my opinion vintage racer/cruiser boats like the Cal 20 are good candidates for a conversion. The reason is all the hardware that is included!
My boat came with way more deck hardware and blocks than I will need for my junk rig. I expect to get the rig up (eventually) without buying any additional blocks, jam cleats or rope clutches. I will likely have several left over for spares or to sell on ebay.
Scott.