3905 FLM chassis w/hybrid bulks...
 

If I use the FLM 3905 chassis in combination with the FLM hybrid bulks + HB diffs, will the center dogbones that come with the chassis fit?

They should do, but since the diffs use a slightly fatter and longer input shaft compared to stock, you may just need to grind the tips of the dogbones for clearance (no biggie, had to do it with my Gorillamaxx when I went to UE ultralite diffs).