Hi,
Nice question. As I can capture your process is neither A&D and nor very much discrete. In A&D type of industry its always better to use ETO. But as you have mentioned you are not in Big aircraft manufacturing and rather small carrier manufacturer, its better to use alternate BOM. Variant config adds a lot of complexity in the systems s well the products are changing rapidly.
Strategy 81 and 82 directly allow you to create planned and production order from sales order. You can use it. But what about MRP run. If you are with MRP then use a different strategy. Else it is fine to use 81 and 82 (As they don't use MRP).
Hence process in MTO with discrete manufacturing.
Hope this helps.
Thanks and regards,
Krishnendu.