Thanks... basically any 180 crank set will do, even a road one but u have to play a little bit maybe to make it work, all depends. Regarding the chainring just put a road one, it will work fine, The ramps are for shifting u are not shifting, a road chain or a track chain will work fine as long as the chain is wider than the cog and the chainring you should be ok.

Looking at the crnkaset u have and assuming you have the matching BB I would try to get the same set of cranks but longer. The issue here as somebody mentioned is that for single speed or track or really rare to see those 180 mms cranksets. But u might be able to find them for a road bike. The chainline will change maybe a little bit but since i dont know what wheelset do you have i cant even take a guess but probably it will work fine.

If i was you i would play with the chainring 1st. Then start planing for longer cranks once u know exactly what u need because we are taking shoots in the dark in here. W/o knowing what u have makes it harder sometimes.

Thanks,