Get the book "The Gun Digest Book of Firearms Assembly/Disassembly Part IV: Centerfire Rifles Revised Edition" by J. B. Wood.
These are tough guns to put back together because the lever has to be timed to the bolt due to the rack and pinion design of the bolt closure but Wood covers that in the above book (page46).
I suggest that you spread the negative word on the gunsmith that failed to put your BLR back together. He obviously is not a real gunsmith if he can not even find the literature to help him get it back together for you, especially when he took it apart. And what other gunsmith would not take on a gun in the condition of your BLR? I would think good business practice would be to help the potential new customer and charge by labor hours rather than a straight fee and for whatever parts go missing or are broken. That is nothing more than good business practices. Shy away from those gunsmiths too!