If you want to make a SFC/SNES portable, you'll want to get a 1Chip motherboard (a later, more compact revision). The original motherboard has a few obstacles to trimming - too many discrete chips, and the audio circuit make the resulting trim pretty bulky.
1CHIP motherboards are found in later revision SFCs and all SFC JR systems.
I'm not an expert in this though, so you'd have better luck seeking YveltalGriffin's advice : P