Packet sequence numbers

I’m using a vector-insert block to add a fixed-size header to a
stream of interleaved short samples at a fixed interval, and
then running it though

stream-to-tagged-stream => tagged-stream-to-PDU => Socket-PDU

to wrap it up in a UDP packet and send it out the network.
The header consists of 28 shorts, and the data of 512 shorts
(actually 256 complex short samples), to yield a UDP packet
payload of 540 shorts (1080 bytes).

This works fine for the fixed fields in the header, but two
of them are variable: Sequence-number and timestamp.

Is there any convenient way from within GRC to insert an
incrementing number into one of the shorts in the header?
I know it can be done by writing a custom block, but is there
any way to use existing blocks from within GRC?

And what about the timestamp? Any easy way within GRC to
use and track the timetag from the USRP and the sample number
to gen up a timestamp value for the header?

@(^.^)@ Ed