What if you tried 2 units of the FBelly/Leadies combo, and one unit of 7-8 leadies with a BSB with the Flaming Banner?
That way, you get lotsa flaming attacks, and the big batch would utterly decimate any regen or flammable units! It's kinda risky for the BSB, but if you're doing a gunline anyways, might as well, right?
Then, do 600 points of Gnoblar trapper bunkers (12x10packs), and with three Sabres, you'll be plugging up the mainline while the Leadies fire away
Throw in the two Ironblasters to put an end to their artillery, and back it all up with a Heavens Slaughtermaster general (hm but then you'd need the butcher tax... are you planning on making one of the FBellies the general?)
I've actually been pondering on making a gunline list. I hope some of these ideas help out a bit