Modeling of the right atrium with extension of the inferior/superior vena cava and tricuspid valve

Hi, For the project, I will need a model of the right atrium out of a patient-specific heart image that will be provided. A prototype of the model is also going to be provided. Essentially, I need the model of the Right Atrium of the heart to be 3D printable, hallow, the added inferior and superior vena cava (you will get the idea through the prototype provided), the added extension for the tricuspid valve (also provided). Here with the tricuspid valve, there will have to be made a little niche, where a mechanical valve can be fixated, the idea on how it will have to look can be seen in the prototype. The issues where I need the help from you is that my modeling expertise is not well. The extensions went inside the Right atrium when they should have ended at the plane of the RA but still going through in that sense. The sized and diamters will be provided. The RA face has to bee smooth as seen on the prototype as well while still maintaining the symmetry and size. Prototype file can bee seen in the attachment as well as the singular Right Atrium that the work has to be on. Attached documents: The RA and the prototype you can lean on.