In general, you obviously the mobile home needs to be removed from the land. There may be a company that will remove it for a lesser fee for the scrap value. Being built before 1970, there is hazardous waste mitigation. I would suggest you find a company through Bing or Google. 1-800-got-junk may be able to point you in the right direction.
I would not put a modular home on it, but would sell the vacant land. The vacant land has more value than the land with the mobile home on it, because removing the mobile home is a cost. You could list the home with the mobile on it and discount the price accordingly. Then the new buyer, who may have better resources to handle the mobile home, can take care of the problem.
Or, if you have the resources, build on the land and then sell the improved property. What you build depends on the neighborhood comparable properties and zoning.
If you don't have the resources to build, but have the resources to remove the mobile home, do that first, because it will improve the sales price of the land.
i have worked a lot with developers, investors and builders and would be happy to answer any questions you have, including determing the value of the land. Or depending on the location, I may have a potential buyer.