Keep the fuel tank full
Fill the front tyres with water
Get the slightly bigger wheels/tyres of a 35 and fill with water (even heavier)
Get a set of wheels/tyres of the flotation type commonly used in the 80s, used on trailers muckspreaders etc..which are even bigger - and fill with water....just make sure you get ones with the right stud pattern and an offset that fits. (shouldn't be too difficult ive seen plenty with them on) (even heavier !)
A standard accessory for the fergie was front wheel weights which bolt through the holes in the wheels. They come up on eBay often enough.
You can also get front bumpers for the 35, I suspect they will fit a grey fergie too, you can then add standard weights, or have a tray made to add weights to.
Have some one make a front weight tray which bolts into the holes under the front, or on to the front axle, might be cheaper then standard accessories which can now fetch a premium due to rarity