Ahh... Executioner with
HB and Stubber.
The Executioner Cannon is a very large Plasma Cannon represented in the rules as equivalent to a triple plasmacannon.
So a good “
wysiwyg” starting point would either be the Ex Cannon itself, or Three linked
PC. You might be able to source several Russ sponson Plasma Cannons, that you could cut the “sockets” off of, and make a Hurricane Bolter inspired “arm” for the Crawler. If there’s an appropriate flat hull space, you could probably cut the socket off of a Russ
HB as well, to attach at that point. From there, stick a Stubber most anywhere.
The crawler, based on pictures, looks like a reasonable size comparison. Might be a bit taller but that tends to be more of a hindrance than help in 8th. I think it would be a reasonable counts-as.