can any help me for metric screw cutting on monarch lathe

i bought a monarch 16" lathe of actual swing 18.5" serial no 31792. it is having 4 tpi lead screw.i am cutting threads by quick
change gears to select thread pitch. right now i am cutting 12 tpi which is around 2mm pitch the exact tpi for 2mm pitch is 12.7 which i can't get in the machine right now.i have checked the gears of head stock and the lead screw driving gears.the lead screw driving gears are mounted left hand side of the head stock.there are three gears one like qudrant gear of 35 teeth an ideal gear of 25 teeth and a lead screw driving gear of 50 teeth.the 35 teeth gear is directly
geting the drive from the head stock.i think there is little space for the 127 teeth transposing gear.i need to cut 1.5 ,1.75 , 2 , 2.5 ,3 , 3 ,3.5 ,4 ,4.5 5 ,5.5 ,6 mm pitch. pls help me.

I can think of three choices of gear ratios that can get you metric pitches from an imperial lathe.
ratio = drivers/drivens
ratio = 100/127 result = EXACT
ratio = 37/47 result = 0.02% error (i.e., 1.0002 mm instead of 1.0000 mm pitch)
ratio = (4/3)*(13/22) result = 0.06% error (1.0006 vs 1.0000 mm)

My Colchester Chipmaster does it using the last choice. The actual gears are 33t (spindle) meshed with 55t on the same shaft as 65t (quadrant) meshed with 66t (gearbox input). In other words, the 55t and 65t gears are compound gears on the quadrant. Just substitute 37t or 100t for the 55t gear and 47t or 127t for the 65t gear to get the other two choices. You can take care of things like the 4/3 in the last choice via the QC gearbox. The QC gearbox will give you 0.5, 1.0, 1.5, 2.0 mm, etc.