Marinate the pork with the mixture of minced garlic, salt, calamansi juice, pepper nad orange marmalade overnight in the refrigerator.
Wrap the pork in an aluminum foil with the marinade and place on a tray and roast in a preheated oven 350 °F for one hour. (For every kilo of pork you need to roast it for 40 minutes so a 1 1/2 kilo of pork needs 1 hour to cook.)
Remove from oven and open the foil and roast again for 30 minutes or more until brown.
To make the gravy; Combine water, beef cubes, soy sauce and drippings from the roasted loin and bring to a boil.
Make a slurry of 5 Tbsp. cornstarch and 1 Tbsp. water and pour over the boiling mixture to thicken the gravy.
Slice the tenderloin and place in a platter. Serve with gravy.