White LT-1850 Mower, Lawn and Garden Tractor

The OV691EA-600833 engine should work for you if you have the same shaft size. Some of these units had a Briggs 407777-0128 with a 1" X 3-5/32" shaft. You cannot directly interchange the Briggs and the Tecumseh engines. You will need to stay with the engine brand that you currently have.