So 9 months ago I met a small time mechanic who offered to work on my 1955 Chevy in his free time for a small price. All he had to do was take out my old 6 cylinder, drop in the new V8 and that was it honestly. He went on to say the power glide transmission wasn’t going to work with what I believe is a small block 285 V8. Now I don’t know a ton about cars but he then took my engine and transmission and has been trying to custom adapt them to work.. I don’t know if that’s true or not but now he won’t return my engine. I have paid him half of what we agreed on nine months ago and i have the receipt and all our text communication but nothing was written in contract. Should i report it stolen?

TLDR: my mechanic has my engine at his home and won’t return it. Can I call the police and will they retrieve it

Edit. I’m in Southern California