we have a Rocna and it fits fine and absolutlely love the anchor. Occasionally it will tip upside down when raising it into the roller but a boathook is easy to flip and get in up and secure.
We upgraded from a Bruce 40lb anchor to a Manson 60 lb anchor on our B-40 as well as went all chain instead of rope to chain rode. The anchor fit perfectly on the roller. One suggestion is to put an inline swivel on the anchor and have a boat hook handy to reorient the stock of to release the anchor if it does not align properly when you haul it in. It took me several jams to figure this out as the stock will jam in the space after the roller. On several occasions we had to use the gennaker halyard to relieve tension to clear the jam.
We have a 55lb Rocna on our 43 and it fits just fine, sets quickly 99% of the time and holds like a rock. I use a double line bridle made up of 5/8" 3 strand and a chain gripper plate. On those times where it doesn't set immediately I just let it sit and sink in for a minute or two then retry the set. Very seldom do we have to move to a new spot. We have 200' of 3/8HT chain without an anchor swivel. I find that as long as I pause just as the anchor hits the roller I can use quick clicks on the button to bring it up and over the roller into place with less banging and twisting. On the rare occasion it wants to roll upside down I simply let out a few feet of chain, let it realign itself, then finish retrieving it. When anchoring I ease it off the roller about half way then let it drop fast. Trying to finesse it seems to cause more swing back and bangs on the hull. Fortunately very few and minor dings in the bow. It's a great anchor go for it. You'll sleep like a baby once you do.
We use original 44 pound plow that came with boat. Added 100ft 3/8 ht chain in 2010. This setup has proven very reliable and we have not drug since 2010. This set up has held in numerous weather systems with high winds from Martha's Vinyard Ma to Staniel Cay, Bahama's.
When we replace this system we'll purchase a heavier Rocna anchor similar to Mike's and retain 100ft of chain. The main advantage the Rocna possess , in my opinion, is it sets quickly, and, it will reset itself quickly in certain situations if boat drags ( very important difference). Holding ability is increased with weight of a heavier anchor, regardless of type anchor.
Forgot to mention we have 150ft of rode attached to 100ft of 3/8ht chain for total of 250 ft ground tackle.