I want to try wood arrows off my '69 Bear Grizzly and I'm not sure where to start in spine. It's 48# bow and I draw 26", so I'm guessing around 42#. I thought maybe 35-40 spine? Any help    IJ

I would guess those will work if they are cut short and had some 125 gr heads. My Gizz is 45@ 28 and I draw 27.5 it likes 50-55 cut 29 to BOP with 125 gr heads.

What's your point weight?(nut)

125gr..........ij

If you are using a heavy shaft like ash, I would suggest a 40-45 pound spine, with the arrow cut to 28". If it is something lighter, like Sitka spruce or a tapered Surewood, I would go 45 to 50.

I draw 26.5" to the deepest part of the grip, and just cut all my arrows to 28 as a simple way to keep things consistent. My finger sometimes finds the back of the broadhead when I cut them to 27.5".

Killdeer

I shoot a 45 @ 28" Bear Grizzly and I draw 27", so my actual weight it probably close to yours.  It likes the Surewood Doug Fir shafts 45-50 cut to 29" that I shoot from it.  125 grain broadhead or field point.

RonP