Need number 13. Your pic shows number 2.

www.partzilla.com/catalog/yamaha/motorcy.../dt175c/transmission

Good eye RT325! 

And the shaft in the photo doesn't look like it's the clutch shaft for a 1976 DT175c model...  1976 had a "necked down" clutch stub compared to earlier models. 

P.S.  I've been into dozens of the 175 Enduro cases and find it extremely difficult to assemble the transmission into the left side case.  Much easier to assemble trans into the right side (clutch side) half in my experience.  Just something to keep in mind if you find yourself struggling following previous advice that was given.  Also make sure not to lose any crank shims that may be present.  They like to stick to the bearing or crank and can get lost.

Have a look at the Yamaha manual covering 74-76 bikes, available in the tech library section of this site.

Section 3, page 54 covers transmission reassembly.

thanks again all
so great ti have a resource where people actively contribute and are willing to spare their time to help others!
yes have managed to cancel the order thankfully
looks like i may need the funds foor the axle drive
i will attempt to loosen these stubborn last bolts and split the case soon
noted on all advice thus far
i have been watching

and have found it another exellent resource
i note his shiftng drum comes straight off at 20:16 or so?
as an aside has anyone here had any luck in straightening these shafts?
just a thought
D

I would think shaft would probably snap if straightening was tried on it?

Stuck case screws can be removed using a MIG welder. If you dont have one, try hitting the end of the screw with something like a 10mm steel rod, and then see if the impact driver works.

If not you will need to drill the heads off the stuck screws, split the cases, end then after heating the cases with a blow lamp, remove the remains of the screw with molegrips.

The motor shown in the video is a a DT175MX and the shift drum isnt the same as a twinshock bike.

As your output shaft is bent, you may not be able split the motor in the way suggested in the Yamaha manual. You will then need to press the crank out of the LH case, using a case splitting tool.

If you are in UK, it would probably be easy to find a TY175 output shaft, but not so easy to locate a 5 speed one?

ha yes were getting into Jugaad territory with trying to straighten
forgot about the TY 175 x parts compatability
open the search a little wider
thanks for tip with torch on screws will have a bang at them again today but its not looking hopefull

Where are you in UK? Not sure if a TY gear shaft would fit as they have a 6 speed box?

imgur.com/a/zvOah13

seller doesn't think it will fit but does look remarkably similar, however does have 3 groves on shaft rather than two, reasonably priced and uk though 
...or am i grabbing at shafts here?

edit 
imgur.com/a/cZE79Ri
actually this one is closer match i believe 
D

There’s a brand new one on eBay $39.95 USA I would buy a new one and be done