Steve, if you are running few or no accessories, and the engine isn't loaded with a lot of smog stuff, you will have very few hoses. You can use one of the threaded intake vacuum holes for your brake booster, or use the big hole in the rear of the carb. You can tap into any other vacuum source back there for your automatic transmission modulator hose too.

I would put a breather on one valve cover and a pcv hose on the other so you have cross ventilation, otherwise you will have the potential for oil seeping out of the two breathers, if you went only with those.

As for the internal/ external balance question, pre '78 engines were internally balanced and '79 up are externally balanced. If you aren't sure what year you have, there may be some numbers on the edge of one of the crank counterweights. Internally balanced engines start with a "2" ( like 2 Y, etc) Externally balanced will start with a "3", or have maybe no number at all. Also, the spacer between the dampener and timing cover will be different. An internally balanced motor has just a sleeve there, and the external balanced one has a sleeve with a protrusion on it, like a weight.

Don