Thanks kirill, I played the software HP_3478A_Software_AR488_Arduino_GPIB and HP3478A.exe, they are also interesting but I'd rather use the pure bench meter function, so I made decision not to make an external serial connection. the HP3478-ext I like most, and also I think the most useful function, is conductivity and diode, it is very helpful when doing some repair work.
so I made a simplified circuit and a tiny PCB, it works like a charm! I BTW changed the 4 capacitors as well, now it may work for me for anther decades :-)