I don't think replacing the motherboard will work. AFAIK i9000 and i9001 have different cameras, light sensors, etc. so it will be very unlikely that you'll get a working device. But why don't you just use your i9000?
Sent from my GT-I9001 using xda app-developers app
My Phone: Samsung Galaxy S Plus GT-I9001 running CyanogenMod 10.1[ION + PMEM ADSP] by ADC-Team Release 1 + K^Kernel v1.0 (3.4.74) 378MB RAM by Christopher83, CPU: 192MHz-1824MHz, Governor: SmartAssV2, IO-Scheduler: SIO
My Tablet: Google Nexus 7 (2012) running CyanogenMod 11.0 (latest nightly) + Oxydo-Kernel v15 (3.2.53) by Sgt. Meow, CPU: 102MHz-1600MHz, Governor: SmartMax, IO-Scheduler: Row