Locally, I've changed the members of 'struct msgbuf' from "long" to
"int64_t" to make 'struct msgbuf' compat32 friendly.  I've not had any
problems on either alpha or i386 other than the old msgbuf looking a bit
funny on i386 - I suspect it would fail the magic test on sparc due to
endianness.

Is there any other problems associated with the type change, and
due to the "funnies" above, would I be better off picking a new
MSG_MAGIC (the current one is 0x063061), and if so what should it be?

0xdeadbeeffeedcafe is already used elsewhere, isn't it? :-)

Simon.