timing the same for headers set up? lack power?

The one bbl carb will probably be ok up to about 4000 rpm if it's jetted right. The header and exhaust size looks ok to me, backpressure is for 2 stroke engines like dirtbikes and chainsaws. As for the timing, every engine is different so to get the most power is going to take some trial and error. I would advance it till it pings under full acceleration then back the timing off until the pinging stops. This usually throws the timing off at idle speed so you'll probably have to pull the distributor and play with the timing curve by changing the advance springs.