Hey guys, lately I'm toying with the idea of modifying the front end of my NPAP to be like an AK104.

One thing I'm concerned about is the change from a 45 degree GB to the 90 degree FS-GB combo. Would the change cause cycling issues?

I've seen the Bolton combo with both 45 and 90 degree ports. But it being secured by a screw has me apprehensive.

The only issue you'll probably encounter is that the 90 degree gas block will sit further back relative to the original position of the current gas block. This will cause other issues with fitment of the gas tube, which would require it to be cut down, possibly to the point that it would need to be re-flared at the end. Also, keep in mind that the M70 pattern front end uses a longer than Russian standard handguard, so you won't be able to install 104 pattern handguards without installing a new handguard retainer and re-cutting the barrel for it. This would also leave the previous hanguard retainer slot exposed if left as is.

Thank you, I hadn't considered the necessity of cutting down the gas tube for the conversion.
Is it possible that would be unnecessary with an MI railed gas tube? My understanding is that they are cut slightly short with the intent of having a nut at the end used to adjust tension.

I'm aware of the different handguard sizes. I have a Hogue foregrip on there. So that with the railed gas tube and I suppose the conversion would more appropriately be called AK104ish.

probably not what you want to hear, but it would better suit your needs to start with an SGL or 107F for this. It's a direct replacement (if using Bulgarian 104/105 combo) and is easy to do. Just my opinion though.

Why not just keep the gas block and move the rear sight?  AKA Kreb's style?

Having never handled the MI gas tube I couldn't say for certain. Also, you'll need to turn the barrel down to fit the combo block as Yugo pattern barrels are too thick.

As to your main question that I completely missed, you should not have cycling issues due to gas if the ports are aligned to each other.

The thought had occurred to me to sell this rifle and save more for a factory rifle built closer to what I want. That would be far easier and probably the smart way to go if I consider resale value.

But the insight from others is why I posted here before doing anything to the rifle.

I hear ya. I have seen some people do some really nifty innovative things before on this board. Just because it's hard doesn't mean you shouldn't. I'm feeling a bit more philosophical  after lunch I guess.

I don't think I would do this sort of project on a PAP, but all that is important is that the gas gets to the 90-deg port, and the size of the port in the barrel is not changed or otherwise occluded by the port in the  new block.

I have seen guys on AKfiles even heavily chamfer, or even drill a slight angle forward into the 90-deg block so that the gas port in the barrel and very base of the 90-deg port in the block sort of ends up looking like:   <

Let's be perfectly honest here, there isn't an AK on the planet that wouldn't function just fine with a little less gas getting to the piston.  

While it would be an interesting look, and certainly very Khyber-ish, OP, it may be best to just start with a closer rifle as previously suggested.  It doesn't sound like there's a ton of AK building experience in your pocket, and this could very quickly become a much bigger and more expensive project than you originally intended.  $.02