The Dr. factory store in VT told me they went from brackets to welds in a few places as the earliest version of the 3PT came to market. They said there is a new version of the string line holder that comes with the current machines being sold now, but the item is back-ordered currently. The new line holder is designed to keep the string in place better than the prior design. It is retro-fittable to machines built before it was available.
As far as attaching a Beaver blade with chainsaw chain attached, the 3PT Dr. mowers don't have the clutch and bail-bar that the walk behind and self-propelled units use, and without that and some sort of added bracket to keep the blade from cutting into fence posts there is currently no provision for the Beaver blade idea to be used at this time.
I suggested they make the necessary changes to upgrade the machine to it's full potential by adding a cable control similar to the mowers they make that tow behind an ATV or lawn tractor. This would allow for disengaging the blade and then they could add a bracket to keep the blade away from posts.
FWIW, another completely different approach that may work for many is the following:
Cutthat.com | Sabre Samurai a front mounted bucket, small sized sickle bar mower controlled by a aux front hydraulic circuit. It might serve the additional uses of a grapple, or angle capable snow blade, etc.
I forgot to mention, the Samuri also allows 110 degree of adjustment to allow for cutting ditches, as well as hedges, vineyards and overhanging tree branches up to 1 1/2" in size. That gives it way more usage possibilities, IMHO, than a big 3PT driven single use machine. Note: I am in no way associated with either company, just expressing my personal views here.
Food for though to alternatives for different uses/needs. :confused3: