I have done similar but one 5gal cream can and 3 gallon sparge pot with close to 9.5# stove top for several brews. Used nylon paint strainer for grain mashed in 5gal and rinsed in 3gal. Stirring is essential in both mash and rinse. Even after all said and done I had to boil some wort in separate kettle as the 5gal was not big enough to contain it all. And honestly some of the best beers I have made were done this way.