Help needed servicing 1990s FIR rear hub

[bencook]

Hi. The bearings in my rear wheel are making a bit of noise when out riding. I can get to the two bearings in the freehub body, but it looks like a need a special tool to access the bearings in the FIR hub itself. They date from early 90s I think.

Any ideas what tool I need? Any DIY hacks I can use instead?