Wow that's a beast of a chainsaw and some serious setup you have. I've got a few 12"-15" english elm boughs that I need milling but I've only got a Stihl 230 so I expect it would be easier to take them to a local mill for processing.It's a Logosol M something or other, it's raining so I'm not going out to look.
I use a Stihl 880 with a 36" bar on it and with the bed extension I can mill 11m long. The timber gets stacked onto the larch bed with the timber trucks crane, and I can then move it onto the mill by hand.
I also have the attachment to bolt the track onto the log, which is handy for very large stems up to 6' in diameter. The Alsakan mill attachment is very good for boards and cuts very accurately if the first cut is flat.