Take the pork should and cut into large cubes/strips that will fit in your grinder, fat and all. Place the chopped pork in the freezer for about 30 minutes. Cut the ham into large cubes/strips that will fit in your grinder. Mince the garlic and mix into the ham chunks, place in the freezer for 30 minutes.
Preheat your oven to 150 C. Set up your grinder. Remove the ham from the freezer. Grind the ham with the finest grate on your grinder. To the ground ham, add the salt, sugar, and corn starch, mix with your hands. Remove the pork from the freezer, add the ground ham to the pork chunks and mix in with your hands, then grind the pork with the ham mixture with the finest grate on your grinder. After grinding, give it a mix with your hands as well.
Pack the ground meat mixture into a loaf pan and cover with foil. Place the loaf pan in a large baking dish and fill that dish with water to 3/4 full. Carefully place this in the oven and cook for 3 hours, the target internal temp of the SPAM should be minimum 68 C at 3 hours.
Take out the baking dish carefully and remove the foil on the loaf pan it will be full of fat. Carefully drain this off (you can save this for fried potatoes if you like or discard). Cover the loaf pan loosely will foil, set another loaf pan on top and fill with weights, like bricks that are covered with foil, etc, place this in the fridge overnight. The next morning, the SPAM is ready for use. Slice, fry, enjoy.