I'd recommend using smitty if at all possible, it can alleviate most of the command line headaches, here are the procedures I use to restore an existing client via NIM/mksysb:

1. On NIM, put the client (name and IP) you want to restore in /etc/hosts
I.e. 10.1.9.29 testaix

2. From “smitty nim_mkmac”, define NIM client on the NIM master:
I.e. testaix
In “Kernel to use for Network Boot”, use “mp” for multiple processors server or “up” for single processor server

3. 4.From “smitty nim_mkres” choose > mksysb, then define NIM mksysb resource: I.e. aixrestore
Use “Master” in “Server of Resource”
In “Location of Resource” field, use the mksysb you would like to restore from, I.e. /mksysb/testaix11012007

4. From “smitty nim_bosinst” Select the client you defined in #1 (testaix), choose > mksysb, then the mksysb resource you defined in #2(aixrestore), and choose the appropriate spot level: I.e. spot52/spot53 (use the spot level of the OS you are restoring)
And make sure of the following setting:

FORCE PUSH the installation: NO
Initiate reboot and installation now: NO

From there I reboot the client and go into IPL, setup the parameters and boot/install from ethernet, works flawlessly.

I suppose you could setup theses screens and then view the commands to get the syntax you need as well. Hope this helps!