The unusual thing a person needs is a reverse ARP server. Normal ARP is where you have an IP number and want to get a MAC address (for some other machine on your LAN to which you would like to send a network packet). Reverse ARP is where you have your own MAC address, and would like to ask what IP should be associated with that MAC address. These days that sort of thing is handled by DHCP, but these old suns predate all of that.
After you have this set up, you need a TFTP server, which is the usual thing I always use to boot bare metal executables.
If you wanted to continue on to boot NetBSD or SunOS, you would need to set up NFS to provide an root filesystem (and other filesystems), and that would require a bootparamd server and perhaps other things I have forgotten. But I have no intention of going beyond a need for a tftp server.
The above NetBSD install document is one of the best resources on sun3 diskless booting you are likely to find these days.