I have a hickory slat and osage board from 3Rivers

I can taper the Hickory and the osage
I would like to build a wider bow than I usually build maybe 1 3/4" at the fades 1/2" at tips
12" riser glued to belly like this one
 

68"NTN some reflex and flipped tips
45/50#
with the osage and hickory tapered I can heat treat the osage before glueup and tiller from the sides after glueup? yes?

What thickness and Taper should I use for both????????????

That's too wide Mark. You wont have any osage left by the time you tiller it to the weight you want, and length. 1 1/2" max at that length, 1 1/8-1/4 would be better. No need to heat treat, and no need to pre-bend the core. Its thin enough you should be able to flex the reflex in with a clamp. Tiller the belly after glue up. Just like a self bow. The back is parallel. I suppose you could grind a 1/16" taper in the osage if you want to. Or, scrap/rasp it off as you floor tiller.

On my lam bows I typically only side tiller, but I spent a lot of time fine tuning the taper to allow that.

I like to build me a bit wide, but I also tend to glue in lots of reflex. I still would only go 1.5" max on the glue up and probably end around 1.375" wide.

Pearlie has probably built 10x more of these than I have though so I'd heed his advice.

I would probably leave the hickory parallel instead of tapering. It's slightly less dense than osage, so it should actually yield slightly lighter mass tips that way all else equal.

Your a glue bow master Benny. I just have preferences after a few.

The Osage is about 5/8 now
How thick should I start
1 3/8" sounds good for width

I like to rip the Osage board so I can get two bows out of it.  I wind up with two 1/4" belly lams.  I make the hickory backer 3/16" tapering to 1/8" at the tips.  A 3/16" power lam (I like red elm, but maple, walnut, etc. is fine) 36" long gives me ample thickness for a 45 to 50# bow.  You can make the power lam much shorter, but it's easier for me to get good glue lines with a longer one.  Last 45# bow I made was 1 1/2" wide at the fades and just a hair over 1/2" thick at the end of the fades.  Nice thing about hickory is that you can always take wood off the backer in a pinch if it's good, straight grain.