Since the stewing meat is in a tin it will have a label with the carbohydrate content on it. I wouldn't expect the carbs to be high unless someone has added something to the tin so I think the meat is probably fine to eat. If you add pastry, it isn't.
The custard is a problem since custard is usually sweet so only a tiny amount or none. If it is in a tin then read the label.
You could make your own custard with Birds custard powder which is sugar free and add a sweetener of your choice or some of the supermarkets do packets of sugar free instant custard
PS I use tinned stewing steak very occasionally as a quick standby meal and have not found it a problem