Worth? I doubt if they are worth the price of shipping.
'Power Pack' heads have a little triangle on top of the square base that Chevrolet introduced on the 1955 Chevrolet. They were introduced in 1956 on only the Corvette, and were a real break through in head design; of course there was only one other head in Chevy's history to compare it to.
Up until 1959 the heads had staggered valve cover mounting holes so if you have an old head you will need special Corvette or stamped steel valve covers. These heads had a casting number of 3725306 and had 1.72"/1.50" valves. The next "Power Pack" head was introduced in 1957 for the rest of Chevrolet's fleet and had casting number 3731539, in 1958 it was replaced by head number 3748770, in 1959 they were replaced by casting number 3755550, and number 3760116, and late in '59 by the 3767465; in 1960 it was replaced by 3767754, and 3774692. All of these changes in casting numbers reflect minor changes in the head casting that had no effect on the heads performance; like a cooling core around the spark plug, or oil drain back hole, or change in the size of the push rod tube, or location or depth of the pressed in stud, etc.
In 1964 the older twin tower (two rectangular bars) truck heads were reworked with bigger valves to make what was once upon the time the "Holly Grail" of stock factory heads; the twin camel hump 'Fuelie' head with 1.94"/1.60" valves. The power pack head became the base head used on every model after that.