will a cosworth vega head bolt directly onto a stock 2.3L block?

The blocks are the same basic design, so yes it would bolt up. But you couldn't run the cam off the stock pulley. The 140 pistons are a lot different too. Some do use the 140 pistons in certain configurations but it requires correct parts and clearance checking. You'd be better off trying to find a complete engine and wiring if you wanted to put a Cosworth engine in. The Fuel Injection requires a lot of special items too.