I would want to know what caused the upper end to fail. The 800's are well known for crankcase/crankshaft issues. If you get the sled cheap enough, it may be worth your while, but cranks are 900 bucks, cylinders, 400, pistons 150... throw in another 140 for gaskets and crank seals, replace the aluminum VES valve guillotines with stainless steel, replace the old VES diaphrams too, that's another 200 or so. Gets spendy quick. You may also have crankcase issues on that engine, a lot of them are out of spec and may require milling and line-boring.
The 800 makes a gob of power, but they are high on maintenance. Go in with your eyes wide open. If you like to wrench, they are prettty easy to work on