Simon- It had an external balancer and flexplate on it when I bought it. I was able to watch it run, on a stand, before I bought it. Only thing I changed from it running on the stand was an external balance flywheel. I've since installed a new external balancer during my troubleshooting as well.
This is the best picture I have of the crank flange. The crank flange is cast with a counterweight on it.
Here is my cam:
https://www.summitracing.com/parts/lun-60105
Here are the #3 and #4 cylinder plugs from last week. BUT, this was just after having the engine warm up at idle. I haven't done a proper shut down after WOT plug reading.
Daniel