Pistol Grip
Like the buttstock, your options for the pistol grip are pretty open. Again, it counts as 1 compliance part so if you choose not to install a US-made grip, you still need to meet the requirements of 922R.
One thing to bear in mind is that most pistol grips do not come with the pistol grip nut. Most of them will have the grip screw, but you will have to order the nut separately. Remember that when you are ordering other parts and throw it into your shopping cart. Otherwise you'll end up paying $8 shipping on a $3 part!
Handguard
The Saiga comes with a plastic handguard. There is nothing about the conversion process that requires you to replace it. In fact, I kept my factory handguards and just had them modified (vents, accessory rail, profile shaping) and I think they are better looking than any of the replacements.
If you choose to replace the handguard, remember that the Saiga set up is different than a standard AK. The Saiga does not have a lower handguard retainer. So in order to replace the stock handguard, you either need to get a Saiga-specific model (TAPCO makes a Saiga Galil-style handguard that includes a retainer piece) or you will have to add a lower handguard retainer.
Installing a lower handguard retainer can be done in two ways. First, you can purchase a two-piece retainer that bolts onto your rifle (around $50). Second, you can press off the front sight block and the gas block and install a standard retainer. The first method is expensive and the second option is a lot of work. I found modifying the existing handguard to be the best choice!
Gas Piston
The gas piston is another relatively easy part to replace. It counts as 1 compliance part. You can use either an AK-47 piston (6 1/4 inches) or an AK-74 piston (5 3/4 in). Just make sure they are US-made to get credit for the compliance part.
Removal of the piston requires drilling out the pins holding it in place. Once the pins are out, you'll probably have to clamp the piston head in a vice to get enough leverage to screw it out. Don't worry -- it won't hurt the piston! Once you get the old piston out, just screw in the new one and replace the pin. You can buy a specific gas piston pin for about $1, or you can use a small diameter nail and peen the ends over.
Bullet Guide
The bullet guide is necessary for proper feeding of ammo using standard AK mags. Saiga-specific mags have a quasi-bullet guide built into them. You can make your own guide (as shown in the tutorial) or you can buy a machined one for about $25. Installation is easy - just follow the directions and go very slowly when tapping the hole. Breaking off the tap is a sickening feeling (ask me how I know!)
Newer (2007) models of the Saiga 7.62x39 have had thicker trunnions - so you may need a thinner bullet guide to compensate. You'll know if you find you have problems getting rounds to load properly.
.
Other Useful Hints
There are a couple of things I wish I had known before I did my conversions. Here are a few to help you out.
Receiver Painting
When you remove the trigger plate, the receiver underneath will be unfinished. I found that Dupli-Color High Heat Black automotive engine paint was almost an exact match to the color and texture of the factory receiver finish. I picked up a can at AutoZone for about $5.
FCG Installation
The FCG is held in place with a spring/wire assembly. GET RID OF IT! There are several easier methods of installation. One is to get a retainer plate. It snaps into place over the trigger and hammer pins and is held in place by the selector lever. They run $10-$15 from typical online stores.
Another option is to use e-clips. They are a little more difficult to install, but still easier than the original spring.
The cheapest (and easiest) option is to get some small cotter-style pin retainers. You can find them at the local home store - just match them to the size of your pins. They install easily and you'll spend around a dollar a piece on them.
.