Stone window ledge installation. How to?

[Codyboy]

I have two, stone (concrete based faux stone) window ledges i need to install.
Need tips and what type of mortar to use.
These things are pretty heavy and not sure how to get it done correctly as to not fall off while the mortar takes a set.
These were never installed when the house was built (2006) because the contractor never came back to finish the job and forfeited the last 10% I was to pay him.
Actually he did put some in those spots but it was a different color so he removed the installed ones but then never came back.

 

[f121]

Got any photos of the spots you’re installing the window sills in? Usually they go in before the windows. I’d bed them on using a standard sand/cement mortar, lift them into place with an assistant and/or a lift.

 

[Codyboy]

Got any photos of the spots you’re installing the window sills in? Usually they go in before the windows. I’d bed them on using a standard sand/cement mortar, lift them into place with an assistant and/or a lift.

In the pic there are 2 blank spaces under the shutters.
Two of the ledges are in place under the windows already.
When I say heavy , I mean for the mortar to suspend them until it sets.
Lifting them is not an issue.

I think the mortar going off memory of 20 years ago was type N.
Does that sound right?