Slowhand, you sound like an old tradesmen to me
Pipe/Steam Fitter myself, anywho...
Your grow setup sounds damn near perfect. Do you have reflective surfaces? (mylar is
best, flat white paint is good, dull side of aluminum foil if you
have too)
Also, your MH light doesn't provide your plants with much red spectrum at all. Plants mostly use the red spectrum of light during flowering, but it still helps vegging and speeds the transition from veg to flower if you have blue and red mixed. You can do with with two separate lights (MH and HPS) or 'go for broke' and get a nice dual spectrum setup. (One large ballast box, one large shade that holds a MH bulb and a HPS bulb)
If you already have an HPS and plan to use it strictly for flowering, I would suggest using both lights for veg and flowering and moving the lights up to keep them around 1 foot to two feet from the plants.
Raising the lights may also help your plants gain that height you want, as plants will always reach for the light to get as close to it as possible. This is why by keeping your light close to your plants they are growing short and bushy, and will continue to grow that way. Whether or not your raise your lights to get them to grow taller is simply up to you and how you would like to grow them. My favorite way to grow short bushy plants is to gently bend all the branches upwards and top the plant when its around 8-16", if done properly this can give plant a canopy effect, possibly producing as many as a dozen king buds. I currently have a perfect example of this in flowering, and will post pics to show you ASAP.