For the 6115CD you'll need a
AAUI to TP (Twisted Pair) Ethernet Transceiver, the follow the instructions below (also dependent on what System Version is has). System 7 isn't going to play nice with MacOS 10.4 and later, but you could connect the 6115CD to the 7300, and then transfer from the 7300 to MacOS X).
For the 7300, Ethernet is the best was to go. Grab an Ethernet cable from your current Mac to the 7300. Now, on each machine setup TCP/IP and Appletalk over Ethernet.
For the TCP/IP setup, assign a manual address of 192.168.0.1 for one machine and 192.168.0.2 for the other. The Mask is 255.255.255.0 and the router address becomes the Manual IP address you gave to the OTHER machine.
Turn file sharing on on your new Mac, go to Chooser in the Apple Menu on the 7300, click on AppleShare, and then, if your new machine's Icon doesn't show up, click on "Manual IP Address" (IIRC), and enter the IP address you assigned to your new Mac.
That's a pretty brief overview. Things may not work for a variety of reasons but in a fair wind, this should work.
Good luck!
