Hey, this is looking awesome! I remember this build from a while ago. I am glad that you are continuing it! One thing that I found which is helpful when trying to find the shape/pattern of an object that has been changed is a super easy/simple technique. COVER IT WITH PAINTERS TAPE!

Meaning if you cover the face section with painters tape then cut along the boundaries it should give you a pretty accurate template. Just make sure that you have at least two layer of tape that are in two directions ie. diagonal and horizontal or vertical so that the tape holds shape. Also, just noticed the comment about Bondo before. Make sure that you are using enough catalyst. You can get Bondo to cure in like 5 mins if you use enough.
The problem with this is that to actually get a smooth finish its better to have a slow cure bondo. But you can avoid this by doing MANY small batches and then after applying dont be tempted to touch it again otherwise you will get the crevices and cracks because of the semi cured bondo.
All the best! I am looking forward to seeing the finished product!
Tank