There are FFs that may work, but they are more expensive.
The Zeiss superspeeds that you probably want, and which might be a logical thing to use if you wanted a set that could mount easily to the ACL, all have the focus ring behind the iris ring (at least my MKIIs do, I think they all do.
It is a generic problem (I think) with mounting a FF to a camera with a spining mirror. With a short lens one can run out of space to mount FF and matte box. Even with ACL, with an oscillating mirror, one seems to run out of space. Wierd really, when you think of all that space that an oscillating vs spinning mirror has saved.
Is Les just being lazy, or trying to make a rod base that he can use for ACL I and II by just inverting the rods on the mount? Such questions. For ACL I there is a lot of space wasted on that rod base. ACL II, the designers never imagined that someone would be mounting a rod base and that the little foot on the ACL II would waste so much space.
Solutions, you could add a mounting hole to that base that shift it rearwards. The access to the power switch is the next issue. One can drill access holes for that in the rod base (I can send pics of mine). Alternatively, the vertical plate can be lowered, and the rods flipped over, so you can reach the power switch from the top, rather than through the front (hole) or in between the plate and the camera (always the lazy designers option)
None of this is hard if you or a friend have some metal workshop skills.
For me, I found that the common geometry for basic follow FFs (and even Arri make them) with the drive gear offset from the gearbox, give a problem with using up available space. Most FFs with a swingarm might work. The drivegear normally can mount either side of the swingarm, so that saves space.
Problem is the cost vs quality. Chrosziel make good ones. Old Arri will not fit your rods and will be too heavy. Some used Chrosziel ones sell for about $1000 sometimes on eBay. Old Cinetech may be OK but where from the parts? Petroff made an interesting one years ago, then stolen by Cavision (he said). Cavisions's offerings looked to have obvious design defects. Then there were the Indians. Proaim made one that looked like a Chrosziel clone. I bought one for $16 recently, to have a look. It would actually be a really usefull tool, but they had put a plastic gear in the gearbox, and a couple of other parts made in plastic that should not have been.
Tilta put out their version. I haven't seen one in the flesh, but the photos look as if the design is affected, heavier than nescessary.
Best advice, wait for a Chrosziel swingarm FF on eBay.
Almost forgot. A good FF design has a way of adjusting gear clearance in the gearbox. Otherwise you have to replace the gears a lot.
Also, With a basic rodd mounted matte box, a Ff with offset drive gear may work, or not. If you have a swing away box then the available space gets eaten up from both ends.
Attached is a pic of ACL II with Les B rods/base (higher than ACL I), cheap FF with offset drive gear. Lens is 8mm Zeiss, cousin of the SSs, slightly shorter than SS. The FF will fit OK, but the swing away MB could not come back far enough.