Sorry about the round versus square issue, I missed that.
Your machine does indeed seem to be a 1973 MTD 143-990, which was a 16 hp machine.
![[Linked Image]](https://www.outdoorking-forum.com.au/forum/uploads/usergals/2013/12/full-2772-13402-mtd_143_990_16_hp_pic.png)
It also seems to have come with hydrostatic transmission, 3 point linkage, and a disengageable Power Take-Off for driving implements:
![[Linked Image]](https://www.outdoorking-forum.com.au/forum/uploads/usergals/2013/12/full-2772-13403-mtd_143_990_16_hp_pic_2.png)
This was a serious garden tractor, not a simple ride-on mower. It would have been nice to see it restored.
