Sure, it will work fine. You will need to trim the barrel on the 22 kit of course, and the 22 carrier will need to be shortened for the PDW length cocking tube. The G3 22 LR kits run great and are very reliable in semi or full.
The only problems are the overall weight and the "small" 20rd 22lr mags. The 308 guns make for a pretty heavy 22 when all is said and done. On the mags, you can try to go the drum and adapter route to get something with a higher capacity. Again, this will add even more weight and my personal experience has been that the drums/adapters can be finicky if not kept very clean and only run with CCI mini mags.
I wish Todd would make good on his MP5 22lr clone project.......
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