All colt 1851 navy frames and standard conversions that I have know of have one piece grips which make them fairly difficult to fit by yourself. If you were to buy any one piece grip online, you will receive three pieces: two grip side panels and a center block that must be glued between the panels to make the one piece grip assembly. The side panels must be shaped to fit your frame and have the correct profile and curvature from front to back. The center block has to be trimmed to fit within your frame and not interfere with the mainspring. The gluing has to be done while keeping the side panels lined up properly.
I think a lot of people have done their own fitting successfully, but it sounds like more than I would want to try.
It would be technically possible to mount two piece grips to your conversion pistol; Ruger vaqueros for instance come with two piece grips I think. If you got two piece grips, you would receive two side panels with a screw to hold them in place. You would need to consult with the grip maker to make sure your grip panels would be able to be fitted to your frame. You would also need to tell the grip maker exactly where to locate the screw, since it's not a grip that ordinarily takes a screw The two piece grips would just not be historically accurate for a conversion pistol. Since the Eastwood conversion is a fictional piece anyway, that might not be such disadvantage though.
Chaz