What grade of oil is used in the forks of a 1991& what quantity

Front Fork Oil cc (right leg):170
Front Fork Oil cc (left leg):170
Fork oil grade:10w
Valve Clearance Cold - Inlet:0.08
Valve Clearance Cold - Exhaust:0.08
Engine Oil Grade SAE:10w/30
Engine Oil Classification API:sg
Engine Oil quantity with filter (litres):0.9
Idle Speed (rpm):1400 - 1500
Spark Plugs Gap (mm):0.8 - 0.9
2 Stroke Tank - Litres:No
Float Height:14 mm

You can use Castrol 10 fork oil which is a mediocre type or Castrol 15 for hard rebound. The quantity should not exceed 250 ml per leg. Cheers

I wouldn't use 5 wt oil.I fell it's a bit light. Proberbly 10 or 15 wt depending on your size.
Not sure about the quantity.It's not easy getting specs these days & Iv'e found most qualified bike mechanics (including me) set them by the fork oil level these days. I must admit however I do prefer the quantity as some forks are outside the golden rule- & of course then you a required to keep up to date with what theyare(some showas commonly)

To set them by level, check the distance from the top of the shock to the oil with the fork fully compressed without the spring. Set this to 110mm & you will be fine
Hope this helps
Regards
Andrew