Welcome from South Louisiana. I Googled your description Feed dogs for Touch and Sew 780. There are lots of good videos and more info than you might need out there. Your part # appears to be 181843 for rubberized or 181843M for metal.
https://www.sewingpartsonline.com/fe...er-181843.aspx This one is rubberized. I have ordered from them before and was very satisfied with my order. They are very helpful over the phone. (888) 824-1192
https://www.sewingpartsonline.com/fe...r-181843m.aspx The metal one.
You have made me realize that I need to check the Feed dogs on my Golden Touch and Sew, Model 750. Haven't sewn on it in a few years. I really need to oil it up and let it run for a while. The sewingpartsonline website says all the 700 series uses the same feed dogs.
Edited to add: Amazon has several listings for Singer 181843 Feed dogs. Several are less expensive than the ones I have listed already.