I'm getting schooled here, on a subject I thought I really knew. The 1960 NHRA rulebook says nothing about gas class cars needing to sit level, and does not have the 24" to crankshaft engine height requirement. The 1968 rulebook states that "bodies and/or frames may not be raised to gain weight transfer" and has the crankshaft rule.
1960: https://www.dropbox.com/sh/2006u57wp7sqpxt/AAC9WnRAsXqmyEgvaR8KYSowa?preview=1960_Drag_Rules.pdf
1968: https://www.dropbox.com/sh/2006u57wp7sqpxt/AAC9WnRAsXqmyEgvaR8KYSowa?preview=1968_Drag_Rules.pdf
More rulebooks courtesy of VW93. https://www.dropbox.com/sh/2006u57wp7sqpxt/AAC9WnRAsXqmyEgvaR8KYSowa