I think you are going about this all wrong.
Presumably, you have done a prototype out of wood, added ballast weights to achieve the sink rate and the action that you are looking for. You were successful and achieved everything you wanted out of your lure. I won't guess at how many prototypes you built, I can only judge on how many it took me to achieve exactly what I was looking for.
Jointed baits are complicated enough, so eliminating all that carving is a very good idea. BUT, it was the combination of the wood density, the amount and position of the ballast that gave you exactly what you were looking for.
Now, you are ignoring the wood density, throwing out all the ballast parameters, and trying to produce a neutral density material, and hoping that the lure will swim exactly as your prototype did.
Swimbaits and gliders are particularly sensitive to ballast. The chances of achieving the success of your prototypes using a neutral density material to replace the ballast is not zero, but not far off.
Roman swimbaits have a very complex ballast system. I know because I have worked on something very similar for a customer. The idea being that you can snip off various elements of the ballast casting in order to achieve a certain characteristic; float, neutral, slow sink and fast sink, achieving these characteristics from a single casting of the ballast.
Do not ignore the importance of ballast or the density of the body material of the prototype.
I suggest that you cast the lightest material available, and then start the prototyping sequence over again using the cast bodies.
Keep the master body shapes untouched for future use. You can produce templates for the drilling operations. There are various ways of achieving the drilling templates that are very efficient.
Sorry if this post seems a little harsh, I really am trying to help.
This is really a more in-depth version of what Mark has posted, one of the most experienced lure designers on TU. Worth reading and paying attention to.
Dave