I sometimes see numbers in parentheses in the structure section of a grammar explanation (ばかりに, for example), but I’m not sure what it means. Maybe that である can replace な in this case?
Structure
Verb[た]+ ばかりに
[い]Adjective + ばかりに
[な]Adjective + な(1) + ばかりに
Noun + な(1) + ばかりに
(1) である