Not a good idea to paint an intake on an XJ, the exhaust heat will flake it off the bottom surface. You can paint an iron head or block, but painted aluminum is going to flake.
Avoid any alkaline detergents like Greased Lighting or 409. Stick to the petroleum based degreasers (gunk etc) for light stuff.
(No conventional hot-tanking either, too corrosive)
Avoid abrasives like steel wool or powdered cleansers too. They'll leave scratches and an ugly haze.
Scotch brite is good only for cleaning mating surfaces like the port flanges.
If you want to cheaply decarbonize the interior of the intake manifold, completely submerge it in automotive grade acetone and let it soak covered for at least a week. I suppose gasoline would also work, but acetone is far more volatile and reactive. If you go in later with engine cleaning brushes, the carbon should come off nicely.
Media blasting is the best for restoring the outside, leaves the pebbly sandcast aluminum looking like new.
If this is too expensive, you could pressure wash it and expect most of the burned on garbage to come off the outside.
