J&J diapers if you get the heat resistant one is maybe 3/16 of an inch at most on the sides and can lay right on the headers. My son and I both run them.

1970 Duster
Edelbrock headed 408
5.984@112.52
422 Indy headed small block
5.982@112.56 mph
9.42@138.27

Livin and lovin life one day at a time