Would I need to upgrade my lower control arms at this point then, before I get the spacers?
Irwin...find out what type of HD springs you are looking at. Are they stock length HD springs, or longer? If they are stock, you may be able to use the spacers.
If the springs are longer, which means they also provide lift as well as stiffer spring rate, then no, you don't want to use the spacers. Longer springs and spacers will make the truck difficult, if not impossible to align. Which is when you upgrade the upper control arms, not the lower.
Think of it like this:
Stock height springs, add spacers for lift.
Taller springs, no spacers and possible UCA upgrade.
Hope this helps!