Well, I've been away and looked in my old copy of Ilford's formulary, and they don't publish the formula for Hypam. I did find a formula for rapid fixer in C.I.Jacobson's book "Developing" however:(posted 8814 days ago)200gms Ammonium Thiosulphate; 15gms Sodium Sulphite; 55ml of 28% Acetic acid; 7.5 gms Boric acid; 50gms Potassium alum; water to 1 litre.
The Potassium Alum is the hardening part, so you should leave this out. 55ml of 28% Acetic acid is about 20ml of glacial, and it's important to only add it after the Sodium Sulphite has fully dissolved.
Other fixer formulae use Potassium Metabisulphite instead of the Acetic acid and Sodium Sulphite. You can also replace the Ammonium Thiosulphate with 250gms of Sodium Thiosulphate plus 40gms of Ammonium Chloride (this makes Ammonium Thiosulphate in solution). The British Journal of Photography Alamanac for 1963 recommends solely using Boric acid as the Acidifying agent. Jacobson also gives the formula for a super rapid fixer using Sodium Thiocyanate, which fixes in seconds apparently.
So it seems that fixer formulae are pretty much mix'n'match really, as long as you've got the 3 basic components.
Silver Halide solvent: Sodium or Ammonium Thiosulphate; Potassium or Sodium Thiocyanate; Potassium Cyanide (not recommended for obvious reasons)
Acidifier: Potassium Metabisulphite; Sodium Sulphite + Acetic Acid; Boric Acid.
Hardening agent: Potassium or Chrome Alum; Formalin.
Have fun.