Do you understand me correctly:
1) NullSoft installer is a 32-bit application that can be run on Windows 64-bit directly. Performs unzip, generates startup files to run UFAND.EXE and the 16-bit runtime and the application starts, but under DOSBox.
2) Application, from which the user installer calls, is another application for 16-bit runtime UFAND.EXE.
NullSoft script contains a control type Windows and decide if it must generate a configuration for DOSBox and launch UFAND.EXE under DOSBox or whether it is sufficient to generate a batch file and run the batch file UFAND.EXE.