IMO, you might want to rethink trading your EV410 for a SWR 410 because the SWR is not a very efficient cab. Do a search for threads concerning this and you'll find several current and former SWR 410 cab owners, myself included, that have found that you have to run a ton of power into them to be heard. The SM-900 would be a minimum. I had a Goliath II and a SM-900 and I would have it cranked and I still got blown away by the guitarist with his 65 watt Fender amp.
How many watts is your EV rated for? EV's are typically very efficient. They're underated as bass cabs. I had 2 EV B115-M's that were really nice though kinda bulky. Don't discount keeping those EV's. Try running the Mesa Boogie 400+ through that EV. I bet you'll be surprised at the sound. If anything, get rid of the 18". The sound produced by an 18 takes so long to develop you have to be quite aways away in order to hear it.
So, my advise is sell the GK and the SWR and buy the Boogie (or something similiar) and run it through the EV, providing the EV can handle the wattage. Of course this is JMHO.