Oh, it's a LOT more... to do the conversion properly, here is what you'll need to do...
1. Remove cocking tube assembly
2. Remove barrel AND trunnion assembly.
3. Remove the stock.
4. Install the forward assist. This requires cutting and welding on the receiver.
5. Install the rail inserts. This requires some fitting and welding.
6. Install PSG1 trunnion and barrel assembly. Yes, it's a lot different from the G3 style.
7. Install the PSG1 cocking tube assembly. This has the correct end for mounting the PSG1 forearm.
8. Install PSG1 bolt and carrier assembly.
9. Install PSG1 trigger pack and housing.
10. Install PSG1 stock.
11. Oh yeah, remove the rear sight from the rifle and weld on the scope mount for the scope.
All in all, it's a major operation and it will commit the gun to the role. In all honesty, unless you have some significant training in long range shooting and can employ a weapon like the PSG1 to it's fullest extent, it's more of a burden than an advantage. It adds about 6 pounds to the weight of a G3 rifle and it's a lot more susceptable to fouling problems.
The conversion will also cost you a few grand to do. If your receiver is out of spec, it won't work unless you have the proper receiver mandrels to bring it into spec.
In all honesty, I'd leave your rifle alone and get an M1A match rifle and use that. It'll be less expensive and it's just as accurate.
Mike