Thread: Best way to attach interior window sill.

Hello, I am new to this website and rank myself as an amateur woodworker. Recently I was given (lucky me) a drop saw and together with my cheap ryobi router have undertaken a project to replace a rotten sash window frame, exterior window sill and interior window sill. 4 weeks later all is going well so far. I am nearly finished! All my cuts are straight! However, I would like your thoughts on how best to attach the interior window sill. Previously the old window sill was nailed at an angle through to the exterior window sill. The nails used were quite thick. I think they may split the timber i have selected for the job. I have elected to use a piece of finger jointed pine 1.8m long by 30mm thick by 85mm wide. It has a bull nose edge. I like the idea of using screws in case I ever have to adjust/move the window sill in the future. About 1.6m of the interior window sill will sit on the edge of some bricks at a width of 35 mm. Behind the interior window sill is the exterior window sill. If I were to screw horizontally through the 85mm width of timber how long should the screws be? Should I consider using l-brackets secured by masonry plugs as well or as an alternative? Any help appreciated? Thanks, NewCut