Without getting in to all the calculations, I'd say just go with the 1 1/8. With 1" t-bars and new springs out back, it will probably understeer a fair amount, but that will come back in to line when you add the rear bar.
Alternative to that would be to use a stock 7/8 bar for now to minimize the understeer and step up to the larger bar when you add the rear bar. Stock bars can be found here and there pretty inexpensively.
BTW, your new leafs are probably somewhere in the 150# range, +/- 10%.
I've honestly never tried a 1 1/4" bar. Although I did use two 7/8" bars at one time in an old race car of mine. It had lots of roll resistance.