It does not foster a good faith relationship with the client to charge them to build a model and then not deliver it because "technically" it wasn't numbered as a deliverable. The client may not notice the oversight until they're ready to use the model again and discover they're shanghaied into either using the same consultant or paying someone else to reinvent the wheel.
If it's for future projects, I'd pad the proposal a little and make a big song and dance of how you're delivering the model for their use, and in subsequent proposals, focus on how you have intimate knowledge of their model. I wouldn't apply too much padding, though (a good model development report as extra deliverable sized padding) as other consultants who were cheaper could amend their deliverables in negotiation stages to include delivering the model.