Some historical RFCs

RFC 717 - Assigned Network Numbers (1976-07-01)
Shows an early version of the IP and TCP headers. IP addresses are already 32 bits, split into an 8 bit network and 24 bit host part.
RFC 739 - Assigned Numbers (1977-11-11)
First list of TCP ports. Telnet, FTP and finger are already there.
RFC 760 - DoD standard Internet Protocol (1980-01)
This looks already very much like the current IP header (RFC 791). The TOS field is a bit different, the TTL is still counted in seconds (instead of hops) and there is still an implicit /8 netmask, but that's the only differences I can see.
RFC 761 - DoD standard Transmission Control Protocol (1980-01)
This looks already very much like the current TCP header (RFC 793).
RFC 762 - Assigned Numbers (1980-01)
First list of protocol numbers. Includes TCP-4 and UDP (IEN-88: Which RFC is this?). there.
RFC 768 - User Datagram Protocol (1980-08)
Current version of UDP.
RFC 777 - Internet Control Message Protocol (1981-04)
First version of ICMP.
RFC 790 - Assigned Numbers (1980-09)
Introduces network classes. 127.rrr.rrr.rrr is "reserved". No class B or C networks are assigned yet.
RFC 791 - Internet Protocol (1980-09)
The current IPv4 specification.
RFC 792 - Internet Control Message Protocol (1980-09)
The current ICMP specification.
RFC 793 - Transmission Control Protocol (1980-09)
The current TCP specification.