Look at what I found
 

So, I'm replacing my head gaskets and the top of the cylinder heads are covered with a sludge type substance. Is this normal?

yeah it's normal for engines that don't get regular oil changes every 3-5K miles.

is it sludge or is it hardened varnish? That looks pretty normal, and not too bad IMO.

It's not really sludge but definitely more than varnish. Be sure you use a HDEO like rotella 5w40 at 5k mile intervals. How did the valve covers look? You may want to drop your oil pan and clean it up and clean up the oil uptake screen. Oh yeah after the job use a cheap dino and change after a week.

Ya that doesnt look that bad really, Ive seen worst.

A couple more photos. Why is it in the intake and only in the front four?

Because your PCV sucks the crank case gases out on the valve cover and into the engine to be burned.
If the PCV is located towards the front of the intake then all the oil will collect on the front half.
It turns black like that on the intake because when the engine is hot and the oil vapor hits the hot metal it forms that varnish/sludge.

This is bad...http://www.carbibles.com/sludge_casestudy.html

Ok, got it. It is nothing for me to be overly concerned with but would using an oil catch can be advised? In a earlier post it was recommended to use a "cheap dino". What's that?

cheap conventional oil like autozone or walmart 10w30, use it for a week and change to a good oil. This will ensure all the crap from the head gasket job is flushed out.

What he said, along with a cheap oil filter, then switch to a good oil filter like a NAPA (Wix) or a Purolator oil filter and use diesel oil and change it every 5,000 miles.
Not every 6,000, not every 5,500, every 5,000.