Due to the all conquering influence on me of the space 1889 'soldiers companion' when it first came out, I went off and built two of these 25mm Tsar tanks from cardboard in the early 90's. They are slightly different from the real/actual 1917 Tsar tank although overall very similar, mine was steam powered of course, with a small funnel behind the superstructure. you get an idea of the size of them by the 25mm figure.
They were armed with a 3 inch gun in the turret and two nordenfelts on each sponson.
I did space 1889 sheets for them using the soldiers companion but after all the effort they maybe only fought in one or two battles. One did survive being in a bout of blowpipe wars and survived surprisingly well (dont ask). anyway, they were made from cardboard maybe 23 years ago and lay about for ages so I sold them last year on ebay for maybe 8 quid each, I was quite happy as they took up loads of space. hope the new owner has some good fun with them wherever they are..