Just one thing to keep in mind. The idea of using turf tires as 'flotation' to go over the top of the sand, is only good for unencumbered travel without respect to traction/weight/ horsepower. If you are pulling a heavy load, you will find the turfs are going to perform like slicks....
Try an inbetween like an r4 industrial tire... benefits of an ag with a bit less agressive paddles.
I've been in road construction for years... my stepdad has been doing road const. since army eng. core back in nam doing emergency runways, etc.
Not a single peice of heavy equipment ( except rollers ) that we have use has come from the dealer with anything but an r-1 or r-4 style tire... ( paddle tread or industrial tread ).....
4wd is going to help bunches, especially with wieght on the front.
That 1720, if still with stock r-1's is a baby brother to my 1920.. almost exactly the same except size.... My stock r-1's have only gotten me stuck once... and it was a wet lake bed/bod/muck...2' deep... I high centered...
As for that 861... are you running filled tires? any front weight? Also, does the front steering have lots of play? If so, he should be able to adjust it... I think the 8n / naa/ 600/800 series all use a similar style steering gear box with steering adjustments on it to tighten it up.
good luck
Soundguy