can anyone tell me deal with converting to single speed and which dropouts can/cant run single, and why. ta guys, blamire.

https://www.sheldonbrown.com/fixed-conversion.html

Scroll about half-way down this webpage. Short answer, anything *can* work, but horizontal dropouts or track ends work best.

Vertical = doable, but PITA (can't get proper chain tension)
Horizontal = yes
Track (rear-facing 'dropout') = yes

u CAN get proper chain tension w/ vert dropouts...its just way more of a b*tch

Keep in mind there are short style horizontal dropouts too.

Short and long horizontal dropouts as well as track-ends are usable for fixed gear. However with short dropouts sometimes you're limited to the size of ring/cog combinations.