After seeing monster moves, the railway gun episode a few weeks ago and then seeing a prog on artillery pieces on one of the sat channels this weekend, I thought I'd see what was out there in the modelling world.
I found a few beasties in various scales, then I found this one...

http://store.spruebrothers.com/product_p/soamt9511.htm

I model the BR Blue period, can I bend the rules that far???
(And its also available in 1/72 {76} and for the completely insane 1/35 < the made up kits is 6 foot long! >)

Looks okay to me, but you would need a special loco to use with it.
My suggestion would be the one of the Diamond Head cover...

http://en.wikipedia.org/wiki/File:Am_I_Evil_(album).jpg

Kev.

Its official I'm in her ladyships bad books, found one on US ebay for £46 inc p&p.
At least I didnt want this one http://www.one35th.com/model/dora-peterShaws.jpg
No that one's not 1:35, its 1:6 actionman sized...