It has been done many times over already. buy the Dell oem 3070. Dell OEM MSI GeForce RTX 3070 Part number = KX61MPlatforms = Aurora R12/R11/R10, XPS 8940, Inspiron G5 5000Card dimensions = Length: 189.48mm, Height: 111.15mm, Width: 1.57mmMaximum Power Consumption = 220WPower connector = 1x PCIe 8-pinPorts = Three DisplayPort 1.4a, one HDMI 2.1Memory = Type: GDDR6, Size: 8GB, Interface width: 256 bitsGraphics bus = PCIe speed 4.0, PCIe width x16GPU = Nvidia CUDA cores: 5888, Base clock: 1.50 GHz, Boost clock: 1.73 GHz
Dear : I have check that OptiPlex 7000MT  can support up to Nvidia RTx3070 Display Card, can anyone have try it before ? And if i want to buy it , which Brand  would you to suggest me to buy ?  Thank for your advice     
Optiplex7000MT / 500W & Nvidia RTx 3070