Pros:
1JZ = MHG stock, block is stouter than the early 7M blocks, head flows better, shorter stroke = higher revving.
7M = more displacement, ease of parts availability means you can go forged for the price of the 1J, longer stroke for more torque
Cons:
1JZ = Less displacement means more boosting needed to move the pig of a MKIII around, less stroke means less torque. Much harder to get parts for (but nowhere near impossible) and requires more work/money to get it in and running.
7M = Needs a MHG, as well as oiling system modifications (replace the damn pressure based oil cooler system). Head does not flow as well as the JZ, so the head needs work to be on par with the JZ.
/thread.