Hi George,
You would require the full blazon if you wanted them done properly - your interpretation isn't good enough. For instance you say,"...the crown ...... appears to be similar to a Marque <sp> crown ..." - what is a "MARQUE" crown? You've got me on that one.
And you go on to say, "... face forward, open with bars and the three plumes." I gather you are referring to the helmet with this description - correct? If so, it cannot be "open with bars" - it's either 'open' or 'barred' (# of bars??). You also mention, "... three plumes ..." - what sort of plumes and what colour/s?
In your first email you mentioned that, "The weapon of both the heerlijkheid Merwede and the line Merwede ..." - to what 'weapon' are you referring? I gather that the arms are Dutch - yes? If so, there should be a full blazon lodged with the granting authority. Have you tried to get them checked out by any of the Heraldic societies in the Netherlands?
If you want someone to render these arms for you, you will have to give the artist all the necessary information of the official blazon, not just your interpretation of it. It cannot be done correctly without this official blazon. If you can get that all sorted out, I can let you have some very good contacts for getting them depicted properly.
Regards,