The Chevy Vega never had a V-8 originally, so are you starting with a kit with a 4 cylinder engine, or a kit with a Chevy small block V-8? One thing you can use is Google Images (or other site), and search for photos of modified Vegas with V-8's as that was a popular mod during the late 70's and 80's. Thois will help in the layout of parts and the mods needed to add a V-8.