I think 3/8" is way too thick for a 28" arrow and a 45# bow. I have 3/8"x30" birch arrows. tapered in the shaftment, for a 55# bow and I think they are a little too heavy. I strongly suggest you will have better performance with thinner arrows.
Birch, ramin, ash, oak, maple, etc. usually are about .55 SG. The average spine for these woods is about 70-80# at 28" and about 3/8". Poplar, pine, cedar, etc. are lighter in SG and so should spine lighter, although you're right they'll most likely need some sanding.
