The previous answers were good advice. A Mondial has a timing belt not a chain. You should be able to change belts with the engine in the car -- normally.... but, if you have bent valves, etc from the broken/slipped belt, you will need to take the engine out to remove the heads for repair. Count on spending at least $2000 in parts plus all your labor. It could run even higher depending on how many valves you bent, pistons or cams you trashed and damage that was done. Even a 1983 Mondial Cab in good+ condition would only be about $25K and you could drive it to confirm the real condition. For that one, if they have ALL the paperwork to verify the prior condition, would probably only be worth about $12K and less if they don't.