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.