I can't tell if what you bought were full height cards. This 710 looks to be the usual short height card for use in the small form factor machines.
Be aware this won't turn it into a gamer PC. It's very dated and of low performance.
I would like to purchase a GPU that will allow me to get started into PC gaming.
Will an asus 710-2-sl fit an Elitedesk 800 g3 sff?
I have purchased other graphics cards before and they have not fit.