If someone is speaking the name of something that includes a number, should the number be spelled out or not? For example...
"I just bought a Mustang Boss 302."
"I just bought a Mustang Boss Three-Oh-Two."
"Mustang Boss 302" is a brand name, so personally I would write it exactly how it's spelt. By the same token, I wouldn't write "Porsche Nine-Eleven" or "Ferrari Three-Twelve-T". It would help with pronunciation, but it's not what the product is actually called. This works both ways, mind you: if a character is using a Five-seven pistol, I wouldn't write it as "5-7" or "57".
In the case of fictional brand names, you're free to decide for yourself whether the numbers are spelled out or not.
If the way the character speaks the number is important, spell it out. If not meh, but either way choose one approach and stick to it. For your narrative purposes does it matter if the reader reads
three hundred and two
three oh two
I imagine that in your example it does matter, and that the latter pronunciation is the one you want the reader to 'get'.
In general, it is considered standard practice to spell out numbers that are part of a name or title in dialogue, rather than using the numeric form. Therefore, in your example, it would be more appropriate to say "I just bought a Mustang Boss Three-Oh-Two" rather than "I just bought a Mustang Boss 302".
However, there can be exceptions to this rule depending on the context and the preference of the speaker or writer. For example, if the speaker is a car enthusiast and is familiar with the Mustang Boss 302 model, they may choose to use the numeric form for clarity and conciseness. In this case, it would be acceptable to say "I just bought a Mustang Boss 302" instead.
Overall, it is a good idea to spell out numbers that are part of a name or title in dialogue, unless there is a specific reason to use the numeric form. This helps to ensure that the name or title is clear and easy to understand for the listener or reader.