On AC plugs, prefix and suffix letters are used to identify a specific type plus the numbers relate to thread size and heat range. R44LTS breaks out as:
R = Resistor
4 = 14 mm Thread
4 = Heat Range
L = Long Reach, 3/4" (19 mm) reach, (14 mm) thread fineline (which these plugs are)
T = Taper Seat
S = Extended Tip

With a stock HEI you can run 0.040 or 0.045 inches of plug gap. A larger gap has the advantage of more complete burn of the air and fuel mixture, but it also takes more power to get a spark to jump a large gap.