Scooterotica

check and re-check your timings before you take the plunge and cut metal.
if your port timings check out you will need to raise that exhaust port as thats woe-fully small.
as others have said minimum 170, i personally would aim for 180+ but this is where you decide what kind of tune you want, and how much else youre prepared to do, as you will probably need to raise your inlet timing to match. gearing and exhaust choice become crucial factors too, and how you like to ride.
to keep things simple you could just raise port to 170/175 for what most call a stage 4 tune.

been on the port timing calculator and running with a 1mm packer,as this made the piston crown level with the bottom of the transfers and ehaust port,the top of the exhaust needs to be 36 mm from gasket face of barrell,so i need to lift it 5.6mm,this should get the blowdown in to the low twenties and exhaust duration of 173.4 deg,don't have a clue what the barrell is off,cost £20 from a parts fair,so won't be end of day if it doesnt work,will let you know how it goes in a few days.

after 1 hour or so with my dewalt drill and a carbide burr and a round file,i now have a not bad looking exhaust port 36mm from top of barrell,
so with 1mm packer i have

exhaust = 173.42

transfer= 128.51

inlet with 1mm
off pistom = 138.08

so blowdown is approx 22.5 deg

any thoughts on the inlet timing in relation to the other ports,i can increase it by taking some more off the piston skirt,chhers all

Why not get you're trusty carbide burr to work on the inlet, maybe widen it a touch at the same time. I think you would want at least 145 for inlet timing, more if ultimate aim is power at the expense of more spitback, higher fuel consumption etc.
Or maybe just leave it as it is for the moment and see how it runs. Remember you can always go back and take more metal off, very difficult to put it back on if you go too far