Beautiful tractor! Hope it works out. A few thoughts since the 401k and home equity options are less attractive.
A) My best rate for a tractor loan was thru a credit union... maybe check online or call one up to see what their rates/qualifications are for used equipment? If you have military status many FCUs operate nation-wide via mail regardless of your residence.
B) If you have a paid for vehicle (or almost paid for vehicle), you may be able to refinance its book value at 2% or less (again, credit union may have better rates).
C) Depending on your credit score and income, some lenders offer substantial unsecured loans.
D) Get one of those airline credit cards and earn a bazillion points, then do option A or B above before the first payment is due? LOL
Whatever you do, may want to act fast. If/when the Fed raises interest rates your payment will go up and/or loans may be harder to obtain.