A couple thoughts
Name dropping on Leftypol is a good idea. That's how I found this place, and it's the easiest way to access users of that site. Probably best to do so in a some what negative way to avoid the wrath of the joonies and to better appeal to people who are already sick of that place.
There has to be something that sets this place apart from Leftypol. I'd figure out what that is and accent it. Just trying to make a copy of that site is bound to fail, since everything else being the same, people are simply going to hang out where the activity is.
Attention is kinda the coin of the realm. So the most fundamental thing is simply having content for people to engage with, preferably stuff that is attention grabbing or generates a bit of controversy/emotional response. People actually love conflict and drama. It's highly addictive, so there's no reason to completely shy away from it.
Ok, post quality shit then. But in the meantime, post stuff that people feel compelled to read or engage with. Hell, post anything. People aren't going to come to a site where nothing is posted for the sake of quality. Moreover, this is an image board. People aren't expecting or even desiring long theoretical treatise.
Finally, add a self development board. A big draw of the right is that it actual promotes improving oneself. Places like Leftypol promote being a depressed, whiny faggot with a bad masterbation habit. Having a dedicated self development board would be a unique selling point of the site. I'd personally get rid of the boards like 777 which seem like a dead inside joke.