If you really need 5cm of spacer and a flipped +17 stem that raises the bars about 6cm more, then you have a bigger problem than head tube length. Even the recreational models only have head tubes that are 2-3cm taller than the racing models.

If you really want sound advice, you need to post your actual saddle height, and your desired saddle to bar drop. I would also need to know what type of headset is used on the frame in question. Integrated headsets are only 8-20mm in height, while conventional threadless models are 25-35mm.

If your saddle height is 74cm, for example, all it takes to produce a modest 5cm drop is a total head tube length, with the headset and spacers, of 165mm. Combine that with a +6 degree stem.