Absolutely breathtaking guitars- world class if I may say so...
Thank you for the kind comments! This guitar building has taken my lifelong craft skills to a new level. A challenging one!!
I would love to post a proper tutorial sometime- but for now, if you can understand from an attempt to explain things clearly:
1) Tranfer your design onto the wood using dressmakers carbon- the finer the "scribing too", like a sharp, hard pencil, the finer the line and the better the accuracy.
2) Use a VERY sharp scalpel to score deepish lines into the spruce- it really IS the secret of neat work- because a Dremel bit, however fine, will produce those furry edges.
3) Use a Dremel with a very fine router bit (2mm!!!) to rout out those channels freehand- please make sure you aren't consuming a nice cup staming caffiene at the same time!!!
4) Headplate material is perfect for the inlay material, if you choose to use hardwood. To inlay those routed channels, you cover that channel with masking tape, and trace the outline of the channel in pencil
5) remove the masking tape, transfer it to the inlay wood, make sure it is firmly stuck, then use a jewellers/peircing saw to accurately saw round the pencil lines.
6) Now the wood might be a little thick for the channel- "resaw" it in half.
7) Now if you are lucky, the peice will fit perfectly- if not, then use good quality sandpaper rolled up to sand the inlay peice. Glue in using preferred glue. Sand flush when inlay is complete.

Obviously any gaps can be filled in using wood dust and CA, or the appropriate colour shellac filler stick. If the gaps are too big, the filler stick won't work.
9) The three most important aspects of this work is patience, a steady hand and sharp tools.
Now you may be wondering why I don't use thin veneer as used in marquetry. Well, I don't get that lovely lusterous depth of sheen in veneer.
Guys, I haven't perfected the technique yet, so I might amend the technique in the future.