Jed,
I bet you would like a springboard on the truck. Its so useful, very occasionally, and takes up little space. Couple pounds. Easy shop fab for a fabricator (not me). I'll ask my friend about making them.
Self-zip...
I canopy raised a dozen long fir limbs on a one-sided edge tree over landscaping, zipped to the drive, solo.
Another time, I did the first portion of a removal of an edge tree doug-fir.
In both cases, I got a lot of height out of removal about 3-4 branches per whorl, as they were edge trees, previously canopy raised and deadwooded.
If you anchor the bottom of the zip-line rope, at the end, you can take your rope to a high-redirection point, where it will have the tail hang down to the work area (Anchor at 0 feet, redirect at 60' back down to working at 40'---uses about 120-150' of rope),
or...
anchor the rope more slightly overhead, if you want, and can have a guy clean branches off the rope periodically.
Sling up a bunch of branches, tension the rope using body weight, and a branch wrap to tie off. All is set natural-crotch friction, so thus far you're still only using one rope. Cut a bunch of branches. As the speedline starts to get more branches, it will invariably stretch, and the effective ground anchor point comes closer to the base of the work tree/ farther from the ground anchor. As this loads up more and more, it will become tighter, to a degree, so you still get some good travel, depending on your set-up.
You can slack the rope up in the tree to advance higher, as desired.
You could even set up two different zip lines to two different anchors, if solo, and needing more horizontal travel.
We natural crotch rig stuff, right?
You can natural crotch zip-line stuff too, without strap and biner.
If you want, I'll set it up and post a pic.
Hope that made sense. I'm posting tired...what's new?. Getting ready to make a list for a camping trip. At least I'm posting from a keyboard. I'll edit later if that's garbled.