Congrats on even getting that engine, v12's are nice, toyota v12's are extremely nice.
I do no know about the compatibility to 1J engine, but a quick search took me to good old faithful wiki
The 1GZ-FE is a 5.0 L (4996 cc) V12 48-valve DOHC engine with variable valve timing (VVT-i). Bore is 81 mm and stroke is 80.8 mm, with a compression ratio of 10.5:1. Official output as per Japanese Manufacturers' Agreement is 206 kW (276 hp) at 5200 rpm although true power output is estimated to be around 230 kW (310 hp). Peak torque of 481 N⋅m (355 lbf⋅ft) is at 4000 rpm with over 400 N⋅m (300 lbf⋅ft) available from as little as 1200 rpm. The fuel injection system is controlled by two ECUs, one for each bank of cylinders. The engine is capable of running on just 6 cylinders should a malfunction occur.
In 2010 the standard engine was revised in order to meet tough fuel economy and emissions standards, reducing power slightly and peak torque to 460 N⋅m (340 lbf⋅ft).
Does it look like the V12 will fit your FJ?
"Because you didn't come here to make the choice, you've already made it. You're here to try to understand why you made it. I thought you'd have figured that out by now." The Oracle, Matrix Reloaded