JR
the Piece-O-Cake is a two channel motor glider. You hand launch it and the engine is only supposed to run for a minute or two to get you to altitude then shut off. Then you you hunt for thermals. I have flown mine a few times for around 30 min's.

Spruce wood will be heavy and hard compared to balsa. Spruce will generally be a white wood like a 2X4 only hopefully a lot smaller. Balsa will generally be a more tan color. Sometimes on the plans there is a picture of the different end grains of the woods.

I will see if I still have the manual down in the shop.

hope this helped
DEG