You could stay with a solid lifter cam and just get a milder grind from Comp Cams along with new lifters. The milder grind would likely solve the low vacuum problem. This might be the most practical approach.
If you go hydraulic you might consider the roller lifter setup. I have it in one of my Panteras and the power band is very friendly. There is plenty of vacuum at idle along with gobs of power when the throttle is opened.
But any of these changes takes careful engineering in regard to pushrod length, geometry of the rockers, and spring rates. These are just examples of the complexities. Converting to the hydraulic roller has additional complexities including the retaining system that keeps the lifters from rotating in the bores.
All of this is actually above my pay grade the experts on our forum can likely provide better guidance.