3.5 v8 inlet manifold replacement and other bits and bobs.

I've purchased a carb and manifold kit from RPI and I'll be doing the job in a few weeks.

Is there anything else I can do while I'm in there ? I've got rocker cover gaskets and valley gasket but as I'm going to be up to my knuckles in the motor so any recommendations for other bits to do?

And is it possible to replace the valve stem oil seals with the heads still on? Or is that a job for when the heads are off?

Thanks in advance for any help and advice.