The Sparc should work out well... since you get a low mount, an absolute cowitness riser and a lower 1/3rd spacer.
If my math is right... The Sparc low mount + lower 1/3rd spacer should be pretty darn close with your hk sights
If my math is right... The Sparc low mount + lower 1/3rd spacer should be pretty darn close with your hk sights