What chainline do you have now? Measure that first.
Are you on the inner or outer ramps?
Is yours a pre or post CPSC spindle? They are different lengths.

You want a 43.5mm chainline. That equates to a 41mm inner, 46mm outer. Lets assume you are now running 44mm on the outside ramp, and you have a 112mm pre-CPSC "Campy pre'94 taper" spindle.

To find an equivalent Stronglight/ISO spindle, you would take your 112mm, add 3mm to make up for the ISO/old Campy difference (that number is from my own experiments), then add double the difference from your desired chainline to your existing chainline (46mm-44mm)*2 = 4mm for a total of 119mm.

You also need to find one that has the same drive-side offset as your existing spindle, or adjust for that as well. IIRC the Campy's are +2mm DS, and so are the Stronglight 118.5mm doubles.

Also realize that close is good enough in the old non-indexed world. Don't sweat it if the closest spindle you can come up with is 3mm different than spec. Divided by 2 that's 1.5mm per side, and I'll bet your components would handle it OK.