Interesting list, I like the fact that you tried to steer around Leman Russes for a change.
One point I thought about when reading the list was: Where is your anti-horde? Usually one sees flamers in some squads. However, then I noticed that your list packs 12 heavy bolters - 36 shots per round - and quite an amount of small-arms fire from lasguns to heavy stubbers. I guess this list could work well! However, the total absence of heavy armour means that your transports will be the target of every
AT weapon on the field; at that point level, your tactics probably should not rely on them surviving very long.
I'm making a fluff-influenced
IG army at the moment, too, and am thinking about how to justify a 60t Leman Russ in my army; however, it should be very, very possible for the Imperial Navy to deliver such weights. There are landers like Warhawk
VI Stormbirds, big void-capable transport flyers that probably have no problem deploying a
LRBT. Therefore, if you want one, get one, the fluff should have no problem with a rapid insertion force that gets a tank dropped with them. Perhaps on very big grav-chutes for style...would look cool.
However, what I was going to say: A naked
LRBT is only 150 points and provides hard AV14 that will probably scare enemies and divert fire from the chimeras. Deploy it in cover and it should live a while, dishing out a S8 AP3 template every round; this should keep the enemy shooting at the
LRBT, while your chimeras can advance (more) unharmed (than without the tank).