I dont know think that the input signals will be your problem, its the output control to the pump module that I would be worried about and whether or not the LS ecu could control the IS pump.
One thing that might be something to think about and might be easier is to graft in the LS pump module inplace of the IS unit.
IMHO, learn to modulate the brakes on the threshold of lockup and due away with the ABS all together being that ABS systems actually hurt you stopping distance. ABS systems only work properly with 100% stock setups. A change in brakes and or tires for the better will not gain the full benifit of the upgrade in tires and or brakes (tires being the main thing here).
ABS systems activate based on deceleration rate, not actual wheel lock-up as many think. Old 1st generation systems did infact look for lookup, but although it was safer then no ABS, it still was not truely effective. an example of the problems with the first systems was lets say you locked the wheels while in a sharp turn (especially at high speeds) the wheel along with not spinning, it also would start sliding sideways, well yes the ABS system would activate and allow the wheel to start spinning, but it didn't recover the sliding of the wheel soon enough. The fix fopr that was to have the abs prevent wheel lockup altogether (i.e. activate before the wheel locks altogether). To do this, they monitor deceleration rate over time (i.e. deceleration G-force). Well this is great if you have stock tires, but an upgrade to larger foot print and higher traction tires allows for higher deceleration rates due to more traction from the tires, but the ABS unit doesn't know this. Basically for example purposes a particular system may be calibrated with a stock setup at lets say 1G of deceleration rate and you upgrade the tires and the new setup will generate enough traction to support 1.25G's of deceleration, well the ABS is still going to activate a 1G so the addition traction avalible is not being used.
Dont get me wrong here, ABS systems are still a very good thing to have especially in adverse weather conditions, but from a performance standpoint, they are not that great.