If the cam was installed 180 off, you would not be turning the engine. The vales would hit.

If you did a valve job, and for some reason, why I don't know, turned the engine over while the head was off, the pump is off. It is going to be much less work to just set the engine to TDC, remove the IP, align the marks on the IP, replace the IP gasket and grease both sides so it does not tear when timing the IP. Reinstall the IP and use the low pressure (drip) method to retime the IP. Remember to do two things when timing:
1) Remove all vacuum lines to IP, and make sure the IP is at FULL THROTTLE (and of coarse the cam lobes are "up")
2) Set the IP at 24-23.5 if you have not replaced the chain. If you have replaced the chain, set the pump at 25. When the chain stretches, it retards the timing, i.e., when you loose much power due to IP pump off timing, time to put a chain in .