the manuals are available as PDF's from the gulfstream web site.
Janes all the world's aircraft after 1983 should give the details as well.
takeoff speed?
well stall at max weight and flaps is given for the G-111 as 105 knots.
1.3 times the stall...137 knots as a takeoff safety speed.
the actual would be above that.
Vne mach 0.85 for the G-111
cruising mach number at full power and max auw is given as mach 0.85
long range cruising as mach 0.77
flap area?
there is a 3 view in janes all the worlds aircraft. scale it off from there.
btw there is a piece of freeware that you can use on a microsoft machine that will save your sanity. it is called convert.exe and has all the necessary conversions in it for aviation use. google for it. you can download it from the josh maddison web site. (josh wrote it)