I just obtained a Black Widow MA II 64" 57# @ 29
Can Anyone suggest what spine wooden arrow I will need.I also shoot a three piece longbow 62" 55# @ 29" it shoots  a 60-65# sitka spruce arrow perfectly.These same arrows out of the black Widow do not fly straight . The arrows are 30" long. Thanks.

Due to center shot and length I'm thinking you're going to need more spine, a lot more in fact.  I wouldn't be surprised if you need another 20 pounds or more.

I think Widow recommends you take bow weight times 1.4, plus I'd add more for the extra length.

If you edit your title to "Widow spine question" you should get some veteran widow shooters to chime in.

Thanks Slowbow I'll try to repost.

some people add to(build out)the side plate, then you can shoot a weaker spined arrow

yogi:
Several ways to fix your delema, as suggested above. build out the strike plate until both bows shoot the same arrows. Or increase the spine for the widow. What I do for my clients is, I add 15# of spine over what the bow weight is and add 5# for every inch over the length the bow was weighed at. So in your case 57+15=72+5 for 30"=77 so using the trad standard of 28" you will need 85-89 spine@ 28"
Bob