Old cassette - what tools

Been into loft - not got old freewheel, so can't work out if it comes apart :-( Found freewheel removal tools tho'

Reckon your best bet is to find a way to get 5spd freewheel off, and replace with dedicated singlespeed freewheel. If you go and buy freewheel from your LBS, they will likely be willing to take the old one off and fit the new one for you at no further charge.

Otherwise, I reckon your sprockets probably simply unscrew (in the normal way). You could try:

• Put wheel back in frame with chain properly attached (but not to smallest sprocket).
  
• Fix cranks into a set position somehow. If you have a big G-clamp, put it around cranks and downtube (or seat tube) to fix cranks.
  
• Using chain whip, try to unscrew / loosen smallest sprocket
  
• Pray you don't trash your fingers when something slips
  Note: would recommend using some heavy duty workman's gloves, just in case