I want a upper receiver that accepts standard AR barrels, BCG, gas tube, etc. But that works with the hk 416/mr556 handguards. I like the raised height of the receiver and love how the handguards mount.

Surely somebody making them could sell them for cheaper than what a hk (or hkparts brand) upper sells for, plus the cost of having it converted to ar barrels.

While I'm sure it would be possible, I've never heard of anything like that being produced.  Most uppers are based off a forging and to get that taller rail height, I'm sure a standard forging would not work.

There's also the issue of parts comparability.  Who the hell is going to want an upper that can only be used with, at max, 3-4 different rail systems (some of which are near impossible to find and expensive as shit when they are found)?  There just isn't going to be a market for that.

Sorry, but I think you're SOL in your quest.

ETA:  If you like how the handguard mounts, pick up a Geissele SMR for your standard AR.  From everything I've seen, the rail to barrel nut attachment is extremely similar.  If you like the height of the upper receiver (for its practical use, not its looks), use a riser with your optic.

I could have a hk upper modded, but was just wishing for a cheaper option.

The only real expensive rail is the Remington arms.  Hk, MI, geissele rails can all be had at similar prices to AR rails. I think troy may even make one?  Some people buy the monolithic uppers/rails, so I don't think fewer choices of handguards is a problem.

I have a mk8 rail now but the hk system is still superior. And with the added height of the top rail, mounting lights and lasers becomes a more slim/compact package.

I'm not disagreeing that there are some benefits to the HK top rail height (especially when it comes to mounting offset lights next to LAMs), but there are some options available that can closely approximate the same thing with a standard height AR top rail.

When it comes to handguard options, people who buy monolithic uppers go into it wanting a monolithic upper for the benefits inherent to that system.  Most people who choose to piece together an upper are probably going to want the wide range of options available for the standard AR platform.

For the record, this is all just my personal opinion.

Geissele rails are what you seek.

Already have a mk8