we were going to do this with pork and spoke to the EH. they told us to do dummy runs with the post so we could check the arrival temperature, they also told us to send it frozen, and vacuumed packed.
we never got any further than speaking about it. we were tempted to buy something from jimmys farm and copy their way of posting meat
the bigger the amount the slower it is to cool down.
goodluck. let us know how it goes.