Pomelos, Grapefruit, and Oranges, Oh My!

We live on a 0.29 acre lot in the southern part of the Central Valley in California. Citrus trees grow very well here, and the original owners of this land planted an orange tree (Valencia, I think), and a grapefruit tree (a sweet ruby red variety). Although the trees are not placed where I would want them to be all the way at the back of a lot that is much longer than it is wide, I want to keep them. The main problem is that I can't even give away as much grapefruit as this tree produces. While I like the grapefruit from this tree, I really prefer pomelos to grapefruit. I know that grapefruit is a hybrid between pomelo and orange, so I'm wondering if a pomelo graft would take on a grapefruit tree. Does anyone know if I can graft pomelo onto grapefruit, and if I can, what would be the best way to go about it? When it comes to trees, I know very basic stuff, like fruit trees need excessive pruning, and it looks more natural if you avoid topping trees. I have never grafted a tree before, so I have no idea how to make it work. I also have not the slightest clue if grafting a pomelo onto a grapefruit would work in terms of actually producing both fruit types. I've been told there's no such thing as a lemon/lime tree because the tree will revert to one type of fruit, either lemon or lime, so I'm wondering if the same would be true of a pomelo grafted onto a grapefruit. Thoughts anyone?

Do a web search on fruit salad trees an you'll have lots of examples of multiple species of closely related plants grafted onto one root stock. As long as your graft doesn't die, it won't revert back to a different species. It's a well recognized technique to fit more varieties of fruit into a small urban lot.

Here's one of the sites online with instructions with photos. As you already have the existing tree, I believe you'll be starting at step 3. http://awesomenessprojects.com/step-by-step-instructions-1-1-1-1-1/