Only use Pine if you can find really tight grain and straight grain material. Most pine you come across will not fit that description.
The problem is that even if you DO find good Pine, it's a lot heavier than spruce.

A virtually direct and exact substitution for Spruce in all respects is Basswood. It's much lighter than Pine, and while you still have to search for straight grain pieces, that will be easier to find in Basswood than it is in Pine.

I've used Basswood for years for all my main spars, struts, etc with never a failure. There's a chart I came across somewhere that compares the various properties of several different kinds of woods and Basswood stands out as being within a smidgeon of identical to Spruce.

Highflight