Help needed with a ported enclosure

I am trying to design a 3 way speaker system and am having trouble with designing the bass reflex enclosure. I have tried using a few programs including WinISD and the enclosure volume it spits out is far too small. The manufacturer recommends 25L with a Port: 50mmø x 179mmL. After putting in the provided parameters I get 7L with a port length around 76 inches! I think somewhere I am doing something wrong but I don’t know what. I am not very experienced and this is pretty much my first set of speakers that I am designing. I have a multi meter and generate tones via a PC and that’s pretty much it. The plan was to get an idea for the box volume and port and try to “tune” it by measuring voltage and hacking off bits of the tube. Ofcourse the details are a bit sketchy and I am not sure when to stop hacking and what frequency is best etc.

Here is what the manufacture published:

Specifications:
Rated Input Power: 60W RMS
Max Input Power: 100W
Impedance (300Hz): 8Ω DCR = 5.7Ω
Frequency Resp: 35Hz-4kHz
Resonant Frequency: 35Hz
Sensitivity 1W @ 1m: 91dB
Voice Coil Diameter: 35mm
QMS: 2.87
QES: 0.28
QTS: 0.25
VAS: 48L
Nett Weight: 2.22kg
Magnet Weight: 848g
Overall Diameter: 205mm
Cutout Diameter: 183mm
Mounting Depth: 85mm

Suggested Vented Enclosure
(Tuned to 30Hz)
Volume: 25L
Port: 50mmø x 179mmL

Here is what WinISD spat out
Driver : c3204
Vas : 43.0
Qts : 0.24
Fs : 34.80
SPL : 90.30
--
Number of drivers : 1
Box type : Vented
Box size : 7.0 l
Tuning frequency : 60.22 Hz
Vent : 1 vent(s)
0.873 m length for each
0.102 m round

I understand that the data publish by the manufacturer is not always accurate and port dimension the computer spits out is probably not going to work in real life. Is my idea of getting and approx size of the box and port and port diameter and manually tune it with a multi meter, 10 watt resister, signal generator and hacksaw a realistic idea? Also I am a little sketchy on the how this manual tuning works so any details on that would also be appreciated.