L67 swap it if you're not comfortable pulling the heads. You can mess plenty of stuff up doing a top swap if you're not very handy with a wrench. Swapping the motor is 2-3 hours old one out, 2-3 new one in, another hour or 2 taking care of little stuff you missed on the install, and getting a gtp pcm with 3.29 gearing plugged in.
This also leaves you with your old L36 to work on, or sell to recoup some of the cost of the L67. You will need to use your L36 flexplate if you go this route, along with new bolts (tty) to bolt it onto the L67. You should be able to get an L67 from a yard for ~$500 without too much trouble.
