Try out True Grain 2. It overlays real film grain over your image, and does a tone curve and color luminescence adjustments to replicate different black and white films. After you edit it in True Grain, you can go back into lightroom and edit it. The photo will act more like a film scan than it will a Raw file, so if you have really dark areas and try to bring them up, they'll just be grey and grainy just like a film scan.
Leica M2 - Zeiss 50mm f2 Planar ZM
Nikon FM2n - Nikon F3HP - Voigtlander 40mm f2 SLii - Zeiss 50mm f/1.4 Planar