IGH need a system to tension the chain. If your frame lack any adjustment, then you will have to use a spring chain tensioner, which is a less satisfactory solution, collecting more crud than a simple chainline..
If you want to run a single chainring, you are better off with a 1x8 or 1x9, simply for modern parts availability. Its better to run these with a chain keeper. I use an old front mech but you can get smaller widgets.
Single chainring cranks are available eg Sugino XD, Truvativ IsoFlow.