I spent two days designing and gluing together the jig to help make the bonnet louver slots. It has a base that gets clamped into a bench vise. The router guide clamps onto a little table on the top edge of the base. The model gets clamped against the vertical part of the base and moved for each cut. That is the fiddly bit as it takes anywhere from ten seconds to ten minutes to line up each cut.
First step in using this jig is to put alignment marks on the model where each louver's line crosses the base of the bonnet. I positioned the top of the back louver on each side of the body, and extended a line to the bottom of the block at 20.5 degrees from the vertical. The louvers are 1/16" wide and spaced 1/8" apart, so I marked 1/8" intervals perpendicular to the first line then used the protractor to extended these points to the bottom. I also taped a 1/8" scrap of wood to the far side bottom to tilt the car slightly to make the side of the bonnet close to horizontal in the jig.
To position the router guide, you need the length of the centre line from the edge of the jig base to the guide's top stop. It is the radius of the router base plus the length of the sloped line from the top of the louver to the base of the model body minus one half the router bit diameter (1/32"). The measurements from the top stop to the base on each side will be the centre line length plus and minus the radius of the router base times the tangent of 20.5 degrees. Mark both of these distances on both inner sides of the guide. The bottom stop slides, its distance from the top stop is the diameter of the router base plus 1/2" minus the diameter of the router bit. Clamp the router guide to the table aligning the side measurements to get the correct tilt for the side of the car you are going to work on. Then mark the centre line of the guide on the edge of the base's table. After that just line up a mark on the bottom of the block with the centre line on the table, clamp and then cut with the router.
Afterwards I did a little work to deepen the side trim groove along the bonnet and then sanded the body and the wings with 150 grit.
Next I will cut the trim pieces and start putting it together.