The Iscorama 54's were made with a rear screw on adapter that covers the protruding element and provides a 62mm mounting thread. Another option I use is three empty 77mm filter rings or two 77mm's and a 77-72 step down to connect the 54 to lenses with larger front elements. As mentioned, the anamorphic alignment is done by pushing a button and rotating the front of the adapter. In my experience the locking mechanism often slips so I always use black paper tape to keep the ring from moving once I've adjusted it.
I have done some extensive tests with my 54 and compared it to just the taking lens without the 54 and in many instances I could not even tell the difference. Both were equally sharp. Where it's character will really come through is with very out of focus backgrounds...and of course flaring if you have a non multi-coated version. It will mount to a 50mm on full frame (I'm using a Canon 5D Mark III) but the edges do tend to display more compression than the center which becomes apparent on pans if you look for it. For this reason I would recommend using a slightly longer taking lens for this type of work.
I had it mounted to my Canon 24-70 f2.8 at one time but do not recommend this as my lens needed servicing soon after. I always used a lens support but I suspect that the incredible weight of the beastly 54 was too much for the Canon lens. That particular lens moves forward and back so it's not a good choice for a heavy add on anyways.
I have found a way to support the 54 that I like. It involves using a Cavision lens support (http://www.bhphotovideo.com/c/product/750371-REG/Cavision_R15_LS25100M_Lens_Support_with_Metal.html
). I prefer this to just a cradle style lens support because even thoughthe focusing ring on my 54 is smooth, it does have some tension and when using a follow focus I find it best to have the 54 locked in position to prevent movement. If you decide to use the Cavision support the trick is, the rear ring that comes with the 54 is a bit too small to work comfortably with the Cavision. RedStan did in fact make a rear ring for the 54 that gives it a 67mm thread and has a slightly larger outer diameter...perfect for mounting with the Cavision support, particularly when built up with a very thin layer of cardboard like those found in a packet of printer photo paper. And the last time I inquired...Alan still had some stock of those rear rings laying around. Of course changing the lenses while shooting is challenging with the 54 mounted with the Cavision so you will want to figure out your own quick release method, or just use a zoom lens that only moves internally. I have my own quick release method but don't have the time to illustrate it now.
There have been questions as to mounting the Tokina achromat to the 54 and it can be done but quite frankly, the 54 is a much sharper optic than many others and the achromat's usefulness won't be as apparent as it is on say the baby Berthiot. When mounting any filters to the front that are smaller than the 95mm front element be prepared for the possibility of a slight reduction in exposure and circular ghosting around the edges in certain circumstances depending on the focal length of your taking lens.
I also notice that my footage with the 54 is smoother than without it, when using a shoulder mount. I attribute this to the added weight. The rolling shutter on the 5D is not good though and seems to be accentuated by the use of anamorphic lenses.