I added 2 croceas to my reef about 3 months ago. Here's my experience, YMMV:
As noted, croceas are rock boring and will adapt/acclimate better when placed on a solid rock surface. I placed mine within the rockwork.
Croceas are a higher light requiring clam. I run 250 HQI MH and have them sitting about midway into the tank (about 13" from the surface).
Both stayed where I put them, but it took a few days of repositioning them after they fell over before they started to put their foot down. What was happening is that they would open and close their shell in response to new stimulii (fish swimming near/over, fluctautions in random current, etc..) sometimes with enough force to topple them over. While this was frustrating, it was important to place them back where they were. IMO, this helps the clam acclimate to its new environment.
After 4-5 days of righting the clam after it toppled over, they both started to lay down their foot. One faces front which is how I positioned him, the other has turned 90 degrees and faces sideways. Since both have established a foothold on the rock, I am just leaving the sideways clam as is. I can still see the mantle fully and if he's happy facing that way (probably has to do with how he fits in the rock he's on) I am not messing with him.
Neither of them truely "walks" (I have a large squamosa that "walks" himself toward the front glass making cleaning difficult, but he is sand dwelling and older), but they did topple themselves over a few times in the begining.
General care for croceas 2" or larger is provide them with enough light for energy production. If you would like to, on occation give them a squirt of phyto every now and then (or just add it to the tank water - the clams will filter what they want to eat). Clams under 2" require regular feedings of phyto because their mantles are not large enough nor mature enough to produce enough energy from light for the clam to thrive.
Croceas are fairly hardy for giant clams and so long as you provide good water quality, good light and a stable environment they should do fine in your home reef.
Hope that helps.