An Ancient Persian Monster - Cyrus War Tower: Build the "Boxy" Bit (Part 1 of 4)

This Black Hat Miniatures (the mold now sold onto Fighting15s/Gladiator Miniatures) model has been hanging a round for a long while, maybe as much as ten years, part of the Cyrus the Great DBA Army project (see below a cleaned up out of the packet and in pieces): 

As befits the chunky casting the wall parts come together with rather gaps manly gaps (see below, it is a product of its time and I purchased it so that it would fit in alongside the rest of my Achaemenid Persian Army - so needs must and I am sure Milliput with come to my rescue):

The worse fitting gaps are at the top (see below, "four walls" of errors compounded or accumulated together): 

Then comes an engineering problem of sorts. I see the war tower, I see the archer crew and driver/shepherd, I also see the bullocks that are meant to pull the war tower .. but I see no means of connecting the war tower with the bullocks? (see below, I was expecting some for of cunning harness): 

While I ponder on such disturbing matters I took Mr. Milliput out of my crafting box and started mixing it between my fingers, then spread it into those annoying gaps (see below, fingers crossed and with a layer of primmer on it it will become one homogenous surface): 

Next Stage: The painting starts.