Richard,
Congrats on your push to SUL. I believe you can find a way if you are willing to continue to play with it and try new things and think outside the box. Often our ideas are lighter on paper, yet don't work out in the woods, therefore, it becomes a trial and error sort of discovery. Here a few ideas to think about. I'm sure there as others, and, these specifically have helped me drop down to sub 80 oz. Maybe something here will work for you as well.
I use a very lightweight trash can bag for my pack liner (0.3 oz). It's very thin yet works fine if taken care of. Worst case they are cheap and you can bring a new one each trip.
For my food bag and hanging system I am using some Zpacks 1.25mm dyneema line, 0.51 CF rock and stuff sack (0.5 oz)
See if you can swap out some of your 0.2 oz Ti stakes with some Terra Nova 0.035 oz skewers. With my specific tarp and bivy setup, I was able to use four of them in locations where I don't need the beefier ones regardless to ground conditions or wind issues. For insurance, just set a rock on it.
A MLD CF Bug BIvy (5.0 oz) has more room than standard bivies and is lighter.
I love the combo set up of a GG Nightlight pad and a slightly modified MLD 1/8" full length CCF pad (total for both 7.7 oz). The 0.75" thick GG gives me some good comfort with proper site selection and the MLD gives me some flexibility of using it many ways (folded in half for max lower body ground warmth, folded in half for more upper body cushion, full length for a little of both)
Bring only 1 pair of extra socks and select a thinner and ankle height version for the backup (1.6 oz). I wash my first pair and wear the lighter ones while waiting for the other to dry.
Use a 1L disposal water bottle (0.8 oz).
Use a 2.5 gallon Ziplock bag (with a zip closure) for your pillow. The bag can also be used when needed to carry more than 1L of water. (Note – this is a recent addition to my SUL kit and has not been fully field tested due to winter arriving here in Colorado.)
Attach a Sawyer Mini (1.7 oz) directly to your water bottle. Lighter than the Steripen and backup batteries (4.2 oz) and, for me, faster and with less potential malfunction issues as when I tried the pen.
MSR folding spoon (0.3 oz) over the spork (0.6 oz)
Very minor and…….Use 3ml bottles instead of 6ml if possible.
If you are wearing full length clothing you might not need sun screen. Take SPF lip balm and use it for both if needed.
If you like Esbit, look into the Trail Design Caldera Cone gram cracker and Foster can set up (2.6 oz for stove, pot, lid, wind screen, and a Zpacks CF stuff sack).
I think you have done an amazing job getting your kit down as low as you have given the weight of your backpack itself. Packs are personal so I understand you may not want to switch and you are close enough that I believe you can still find a way to sub 80 oz while using it. If you do go the route of a lighter pack, I'd highly recommend the Zpack Zero. I have used 2 of these and love them. The latest version weighs 5.4 oz.
Best Wishes.
Edited for typo on water bottle weight.