You are trying to remove the outer lock ring with the four external slots, correct?
I would try and find something the right diameter that I could weld some pieces of key stock to, too make a wrench.
Or this might possibly work,
https://www.amazon.com/OTC-1266-Adjustable-Gland-Wrench/dp/B000X8EGZE/ref=pd_bxgy_263_2?_encoding=UTF8&pd_rd_i=B000X8EGZE&pd_rd_r=8994a111-25b8-11e9-b4b4-51aa5e01cb40&pd_rd_w=DxSS3&pd_rd_wg=FlsHP&pf_rd_p=3f9889ac-6c45-46e8-b515-3af650557207&pf_rd_r=RYKJ8RM663M1RQ1B2RQA&psc=1&refRID=RYKJ8RM663M1RQ1B2RQA
Another option might be a long pin punch and hammer to drive it loose.
Yes that one. It should be torqued to 290 ft/lbs according to the repair manual (screenshot) so im worried about destroying it trying to punch it off if its really that tight.
https://i.imgur.com/mY33hfP.png
Wonder if that is the same tool as used on the older dana axle lock nuts?
Axle LOCK NUT SOCKET TOOL Ford Bronco,F15,GM,dana 44, popular,fits 4 slot nuts | eBay
Otherwise agree with LouNY 4 pieces of square key stock welded to the correct size heavy wall pipe should work
I would try you local auto parts supplier. Take the approximate size of the nut and ask to see their spindle nut sockets.
This style nut is used on many older 4 x 4 front axles and full floating rear axles.
Case IH / New Holland: NUT, RING, Part # 5169116 heres the nut on messicks. Its massive the thread size is m70x2 for the inner diameter