If it's out of the car or the timing cover is off you can use a soft wire brush on the text to get the numbers to come up better if it's covered in crap.
Every chance it could be custom, but looking at Crane's 5L catalogue I'd say that 306 is one or both of the advertised durations. The 888 could be a misread 296 which might make it cam 888341 if it's a roller.
Do you know what kind of lifters it has? Might be worth calling Crane about it.