Sale agreement on basis of will

You have become owner of your uncle's property  by virtue of his registered will so you have every right to transfer your uncle's property to anyone irrespective of fact that property is still your uncle's  name.you can execute sell agreement on basis of your uncle's will.

There is no problem in entering into the sale agreement, you may wait until the name is transferred in the revenue records to execute the sale deed later on, in the name of the buyer.

Wait for proper transfer of title (ownership) of the property in your name.

In my considered view, the property has already been vested with you. Mutation of the property on basis of the Will does not amount to a 'transfer'. It is the well settled legal position that entries in revenue records are primarily concerned with the levy of land revenue assessment and such entries are not absolute as to title to the property. In other words, mere entry in revenue records does not create or destroy rights or title to property. So also, absence of entry in revenue records do not alter or destroy rights, title and interests  already vested in in property by operation of law or acts of the parties.