Hydroboost is the way to go. Hydrovacs are obsolete for medium-duty trucks and are getting hard and expensive to find. All you need is to add a power-steering pump to the engine.
Try to find a master cyilinder with a bore that matches your current one and you shouldn't notice any difference in pedal travel. Look for the chevrolet c3500-c6500 and the Ford f350-f550 trucks in salvage yards.
