Does anyone know of a particular spring that I can use to raise a 66 goat about three inches in the rear and a couple up front?  

hi
U can use higheir dampers that have extra length but 3 inchs isn't alittle.
and also u can mount a rubber spacer under the leaf spring then connect them to rear axle. usully done this to blazer to increase the highth.
for the front u should use a coil spring with extra length  

Get 67 Lemans station wagon rear coils...they will lift the rear a couple of inches...I installed air bags inside the coils also when I want to load the trunk on cruises to keep the height...the only way for the front is the horse shoes that fit under the coils or to use coil-overs which I did...you can adjust height and level front end...  

Try Eaton Detroit Springs, do a search for their site and use the contact info, they can tell you how to measure the current ride height and tell you what it should be stock. Then they can recommend a proper spring rate to get you where you want your goat to sit. Assuming the current springs are original or older replacements they may have sagged a couple of inches and what you really want is a spring that raises the car only one inch above new stock springs, not three above stock.
Steve