First start question reguarding exhaust manifolds

Sure you can, but it is always a good idea to run exhaust before hand so you can actually hear the engine itself. Open exhaust assures you might not hear some noises.

Also, have your timing light attached and ready. When it fires off, run the RPM up to about 3000-3500 and pull the timing up to 36* at that RPM and break it in like that. All too often, new engines are started with retarded timing.