This is getting old. Megarange is just a particular model line in Shimano. Nothing special about it in terms of quality. It does appear be coined as a marketing name for a few freewheels that include large 34 tooth or so cogs. But Shimano has other stuff that have 34 tooth cogs and larger. Not all of their stuff is compatible with the shifters, derailleurs and other components in different model lines of Shimano. Or any other brand for that matter.

As for over sized pulley..... you need to forget such stuff and just look at components that from the manufacturer are said to be compatible. If that component happens to have an oversized pulley wheel, then that's fine. You really don't just go out and buy an oversized pulley wheel to put on a DR that isn't made for an oversize pulley.