Except for frame size - the J-frame is currently the smallest revolver frame made by S&W, and the L-frame is considered a medium/large sized frame - and the mainsprings - the J-frame has a coil mainspring while the L-frame has a leaf mainspring - the two revolvers are very similar. Yes, there are some differences if you are trying to compare a concealed hammer J-frame (Model 640) to an L-frame, but otherwise, in my opinion, the internals should be similar enough for comparison. YMMV.

Good luck,

Dave