I have an Encore with that same LH thumbhole stock. That is the first Omega I have seen with one. That stock is really a nice stock. The one on my Encore was made by Boyd's, and is top quality. I would bet your Omega stock is of the exact same quality.
I wish I could help you more with the exact value. However they keep putting the Omega on sale everywhere. And they keep lowering the price. However Ibelieve the stock(if in good condition-as it appears) on E-Bay would easily bring $125-$200. You should get a good premiunm with that stock. If not I would buy one of the cheap TC tupperware stocks and replace the TH stock-then sell it separately. You should easily be able to find a used standard Omega stock. Just look around. Tom.