Mind if I plop a tweak out and talk about it?
Grey Seer - earthing rod, OTS, screaming bell = 480
Assassin - weeping blade, dragonbane gem = 155
Engineer - level 2, dispel scroll = 125
Chieftain -
BSB, foul pendant, charmed shield = 105
Engineer - doomrocket = 45
43 Stormvermin - full command, razor standard = 371
40 Clanrats - full command, spears, shields, PWM = 285
40 Slaves - musician = 82
40 Slaves - musician = 82
5 Gutter Runners - poison, slings = 90
WLC = 90
WLC = 90
-------
2000
There are certainly better items to give your bell seer, but I kept yours for now - the shard in particular is interesting, though it makes putting the assassin alongside the bell a dicey situation. Oh, and I did bring the assassin back, as you need somebody that can kill stuff in combat, though I guess I'm biased because my bell list uses two of them to great effect (hint: Death Frenzy is your friend, 5 assassin attaks rerolled is too legit to quit). I thinned down your engineers, dropping the toys and making the rocket rat just a rocket rat, who you can now skitterleap alongside the enemy line and let him go nuclear without caring. Partially this is because over 6 levels of magic I just don't think is very useful for skaven, where you have such limited ability to generate additional power dice. On the
BSB, consider his gear totally replaceable; basically I earmarked 35 points for his survival gear and this stuff seemed to work well enough. The dragonbane gem on the assassin could make that 40 points. As your
BSB is likely standing in the front of your only other block, I'd definitely invest in stuff to live.
But right, the main deal is, you needed more models in those two units, so there they are - WFT got dropped in the process but ah well. I say let the stormies push the bell myself, but with this set up you could do either - I guess the benefit of having the clanrats push is that the stormies are a stronger combat unit unassisted? Though of course they'll have the assassin with them and perhaps the
BSB (for what that's worth

). All the same, I push my bell with 45 stormvermin and have had moderate success, probably slightly better than if it were pushed by clannies.
Last thing, I'd keep your gutters far far simpler, with no over-equipped deathrunner. Slings + poison makes them a serious threat to the things they're meant to kill (war machines), as well as letting them help with other things at range (monsters and small units), but 90 points means they can be tossed under the bus if you need to. Really, gutters aren't meant to fight things in combat, unless they're artillery or really weak chaff units.
What lore you thinking for the bell seer?
- Salvage