the original harrows and ploughs were made of wood, a forked tree trunk made a great pough or holes were drilled thru and pegs driven in to make a spike tooth style drag.
i myself am working on making a leveling drag, a pair of 20 foot tall tree trunks, about 3 inch diameter at the base, with three or four 4 foot long cross poles strapped too them about half way down
the long poles will keep the cross poles from going up and down with the surface irregularities and the shorter ones will drag humps along and drop them into the low spots
just a simple easy implement i learned from my elders, i come from a family of farmers
i might suggest that for what you ant to do, try and find some seasoned ironwood or black locust, both are damned hard to work but will wear a lot longer once youve made your project. both woods were used for making pough posts and beams in the past, i made one myself 30 years ago, black locust post and beam single bottom walking plough. after 28 years the beam finally broke, not decided yet if i wanna rebuild it or not, dont have a horse or harness any longer
btw, im also a blacksmith