i would rather use dry heat if possible because i dont want to have to wait a week or two to let the limb dry back out if i use steam.
Although this may seem rational, it is a false statement. Steam bending wood actually dries the wood out (due to the high heat). Steam bending as well as dry heat bending lowers the wood moisture content a lot. This will make the wood brittle once cooled down. You will have to wait for the wood to gain moisture again before you bend it as you would with tillering. I personally think you'll have to wait for about 48 hours, but it does depend on the relative humidity and temperature. With three days, you're probably good to go.
With your guesstimated 90 pound drawweight, I'm having a hard time imagining how far you've pulled the bow. 60# is OK, but at how many inches? The calculation 90#/3 pounds per inch, equals about 60#@18"...am I correct? Either way, you should never pull past your intended drawweight, nor should you ever pull any further than you need to, to spot a flaw in the tiller.
I would need a picture to comment on the need for heat straightening. It may not be needed at all, depending on how the string tracks. The string needs to run over the handle, but any curves in the limbs themselves are just fine, as long as the string runs center over the handle, when you put a string from nock to nock. Osage is said to be easy to heat straighten, so that would make things easier. With a heat gun, you would be able to heat about half a limb at once, which is usually sufficient surface area. You could also heat bend the same limb twice, if needed be.