Damn software that lost 15 minutes of my wonderful typing !!! I'll try one more time now:
I am full of a lot of things so people tell me so I will be full of comments on your post RutnBuck...
1) I bought the first Lane Shark sold in W.Va. It is a great tool and the guys at the company (Travis and others) give excellent support & are very responsive. It is robust with the 17 gpm flow from my MF2660. It needs 12 to 14 gpm in my view. Extremely well figured out. For example it has the right valving to let it free-wheel when you move the loader up or down, etc. Without that the hydraulic motor powered devices on "open center" hydraulics will cause bone shaking screeching halts (and potential damage) when you interrupt the flow by moving the FEL, etc. The Lane Shark is just plain well figured out for all contingencies.
2) I am not real clear on the scope of your task: I gather you intend to clear the combustible undergrowth in 80 acres of dense (probably evergreen) forrest, correct? If this is as large as it might be, then I agree with others -- go rent a skid steer with mulcher on the front !!
3) I do not like the idea that another co. has 'stolen' the Lane Shark design via buying one and then copying it now selling it as a "Trailblazer." Rubs my sense of fairness the wrong way.
4) The guys at Lane Shark sent me a no-cost upgrade when they did the newer blade carrier and bearings design. It is better in being more sturdy but mainly not throwing blades. The new design is bullet proof.
5) Travis (at Lane Shark) has some very good YouTube videos out on using that tool. Worth seeing. He told me a couple years ago that he was considering a mod that would let you adjust the angle (vertical to horizontal) but I do not know if they went ahead with that. It would be pretty easy to do that yourself actually.
6) I cannot accurately picture your majority undergrowth
BUT if it fits the task you may be best off to consider a heavy FEL mounted brush cutter NOT run by tractor hydraulics but rather from a PTO driven hydraulic pump. If you can give up the PTO for long periods while you attack the undergrowth that seems to me to be the way to go. I had one of the very heavy FEL mounted cutters (like a HD bush hog, 3 bladed, hyd motor driven) on my MF2660 initially but my tractor hydraiulics lacked the flow to make it robust. Clogged too often. The PTO driven pump solves that isssue. There are many of these on the market. One example is the "Xtreme Brush Cutter" sold by
Skid Steer Loader Brush Cutters tough land clearing applications which come in 60", 72" and 78" widths. These are serious HD cutters and you just have to be able to lift and maneuver it (you best get the smaller one for a JD4100) AND most importantly provide the flow with a PTO driven pump.
7) A very good option in my opinion (if it fits your circumstance) is to rent or else short term own a medium sized skid steer to drive one of these FEL mounted heavy cutters. The skid-steers tend to have way more hyd pump output than your JD and they can handle the CID or other brand heavy cutters. Maybe use one of those to clear the undergrowth the first ime and then long-term just maintain it with a Lane Shark ? The HD FEL mounted cutters are a LOT cheaper than the forrestry mulchers which pulverize good sized trees.
OK, I quit for now. Let us know what you decide and how it works out. Good luck.