iMac won’t boot. Just kernel panics

So I was running the gm beta for high siera which had apf. I had put off rebuilding back to hfs as I had a newborn and no time to spend at the computer. I have since folliwed the steps outlined in the support documentation and after resetting to hfs the iMac no longer boots from the install partition on my external hdd which it originally did for me to reformat. When I select it it just kernel panics and loops. I tried creating a Sierra install drive but alas the same thing. I tried a internet recovery but the same thing just kernel panic loops. I tried single user mode but the same thing. I have reset the smc and pram but nothing. Last step was to target disk the iMac and installl from my MBP and guess what, when I plug in the iMac to the MBP, the MBP kernel panics. I’m out of ideas and really hope someone has some suggestions.