TexasCHLforum.com

I've been collecting S&W firearms for almost 40 years. This one seems odd as S&W has no record of a 986 in their production catalog in 357. The L frame didn't even exist until 1980, so an L frame in any caliber prior to 1980 is dubious at best.

Maybe you have a customized revolver of recent manufacture? A pic of the yoke, barrel and/or side plate would go a long way in determining it's value, but with what has been shared you are describing something that doesn't exist according to S&W... and if you demonstrate that then you need to go to the S&W forum because someone will likely be waiting with cash in hand for such an item.

A couple of places to confirm what you have:
https://www.smith-wesson.com/firearm-history-request
http://smith-wessonforum.com/