Firearms Engraving Theory and Design Book
https://www.ebay.com/itm/Firearms-Engraving-Theory-and-Design-by-George-Sherwood-Gun-Engraving/202904959870?hash=item2f3e13fb7e:g:BcEAAOSwT7NeRi6c
A Practical Course in Jewelry Engraving Book Ebay
https://www.ebay.com/itm/1940-PB-Spiral-Bound-Book-A-PRACTICAL-COURSE-IN-JEWELRY-ENGRAVING-Albert-Winter/254505394240?hash=item3b41b42040:g:aSEAAOSwQTVePILf
Not bidding high enough for a good engraving block is a vice! But not the kind you want! An engraver without a good vice may end up with a bad case of engravers block! Better yet a good engraver shouldn't be perfect! He/She should have lots of vices! Better to have a good vise than risk...
They will probably tell you to practice simple Scrolls and there backbones 1st before evolving to more complicated designs you are not ready for. Also one of Ron Smith's books on scroll design. I recommend the Advanced Drawing if Scrolls by Ron Smith.
Knowing which engraving projects to turn down is one of the greatest challenges of being an engraver! Thankless jobs! And the costly mistake of engraving an object your best judgment tells you not to do doesn't go unpunished!