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There are many different opinions. This is my personal view based on some good advice from Dan Perry.
You can do some tillering on the belly slat which will give you a good indication of the potential draw weight.
A tillered belly slat can be a good indicator offinal draw weight when compaired to a similar finished bow.
Adding a backing will add around 10lb draw weight. Each inch of glued in reflex will add around 10lb draw weight (not necessarily showing as final relfex but the effectis still there).
So a belly slat that is pulling the same as a 70lb bow just past brace height will weight 80lb if made straight and 100lb with two inches of reflex. Dan Perry advised against glueing too much reflex in,and also advises that asmuch work as possible is done before the glue up as possible, and as little wood removed in final tillering after glue up. Any removal of wood from the belly reduces power whileincreasing reflex (odd but true!). Any wood removed from the backingeven in sanding reduces relfex and loses power.
I would keep the bow at it's current width and depth at the handle. Keep the handle section stright and untapered in any way for about 12 inches in the centre and then stright taper to the tips in both width and depth. I would aim for about 1/2" depth of Ipe at the tips and less than this in width, say 3/8ths. Chamfer and round the belly edges to give it a D profile and tiller for an absolutely even bend. No handle is needed if this is to be a warbow.
Keep the bow the ful llength as shortening it is an option later to raise the draw weight and a longer bow is easier to pull back if the weight is a bit high for you.
Tiller for an absolutely even bend at brace height using a wooden blockor walky-talky stick before even thinking about the draw weight. Once the bend is even take a look at the draw weight just past brace compaired to other bows you have. This will give you a fair indication of the potential. Work out whether you are within target, whether any wood need to come off, what effect the backing and reflex will have.
When ready glue up into reflex and once the glue is well and truly ready take out of the clamps etc. I allow at least twice the manufacturers time to be on the safe side. Be generous with the glue. It is a lot easier to clean glue off than get it into a dry joint afterwards! Sand the bow clean and ideally the bow is ready to shoot! If the bow wastilleredeven at brace height andchecked for strength it should pull nice and clean andeven to the desired drawweight and length. As this is not a perfect world this will probably not be the case though!
Brace the bow and check the tiller at brace using a walky-talky stick and see if any area are stiff or weak. Mark these so you can see them.
I would now put the bow on a tiller tree and pulley system with a good bow scale at the string and pull one inch past brace height at least 25 times. Go back and check the bend. do a few passes with a scraper and clean upwith a fine file. Work the bow 25 more times and check for an even bend again.
Gradually work the bow back, never ever pulling it past the desired draw weight, working the draw back an inch at a time, checking for an even tiller at brace height as well as looking at the shapewhen drawn. I have found that an odd shapedrawn can be checked and verified at brace height. An even shape at brace givesan even drawn shape.
This process will slowly work you and the bow to the point where a good even tiller is achieved at the desired draw weight and draw length or if not give you the best possible.
Keep the bow as well finished as possible. I like to keep mine almost ready for polish.Why have a bow where you want it only to have to lose quite a bit of thatin sanding out careless tool marks.
I reckon you can probably get the poundage you want if you go careful. I have found that Ipe can suddenly change with wood removal so go slow. Changes in density within a stave can lead to lumps and bumps being needed to get an even bend but go for the bend rather than asthetics.
Ipe can take a failry thick bamboo backing. If you flatten the backing so that it is about 3/16ths at the crown and then cut it to match the profile of the pretillered stave and keep it that thick at the tips it shoudl end up keeping your even belly stave failry even once glued up with perhaps some material to be taken off the tips if they are a little stiff.
Good luck.
Mark in England