What you will need.

I'll try to keep it fast and will divide this into two sections hardware & software.

Hadware

The file par_sell.txt which is included in par_hard.lzh has some info in english on how to get the interface kit from the freewing site. The kit includes all of the IC's, capacitors and printed circuit board (PCB). Then get connectors and a power supply, and you are all set. Having an already made PCB instead of designing and etching your own or wraping one, saves you some time and hey! it will also look kewl, so Contact them.

For the assembly process:

Radio shack can supply all of the tools, Soldering iron, solder, multimeter etc. As for the electronics parts, there are some online suplies. Check the links section.

For the Interface:

TTL ICs:
 
1 74HC14
1 74HC74
1 74HC157
1 74HC573
1 74HC574

Capacitors:
 
1 180pF
1 0.1uF
1 100uF16v
1 1000uF 16v

Misc.
 
2 14 pin IC bases. Optional (read text on the assembly process).
1 16 pin IC base. Optional (read text on the assembly process).
2 20 pin IC bases. Optional (read text on the assembly process).
1 AC transformer - 120 to 8VAC 500ma. ( maybe 240 to 8vac. Depends on your area voltage standards).
4 diodes 1N4001.
1 1 AC Cable with plug.
1 Printer cable. Check/Ask it contains the necesary number of wires (18+) before u buy one ( read the PC to freewing cable section).
1 D-SUB25 Pin ( this plugs into your AR/GS).
1 pcb ( see notes on pcb considerations ).
- several feet of 22 gauge wire. Not cable (read text on the assembly process).
1 feet of termo-fit isolation straw. or isolation tape (read text on the assembly process).
1 case. your choise.

Software

Once you have successfully acomplished the assembly part and ran all of the tests, you will need the following to perform a "Live" test on your new Interface.
Since we will perform only a very basic test wich will show us if everything was done ok., we will only be needing caetla. So get caetla 0.35 from K-comm.'s site. Make Sure you get caeflash 1.0 or higher.

Sure you will want a C/C++ cross compiler and/or assembler target the R3K once everything is functional, but then, again check the links section to supply your needs.