59mm throttle bodies can be used on non-ported factory intake manifold. 65mm throttle body requires a ported upper intake, or a 3500 upper intake and adapter. 68mm throttle body can only be used with slightly ported 3500 upper intake. A ported 3400 upper intake is not big enough to use a 68mm throttle body without major modification.
Core charge of $150 is for the stock PCM and the throttle body. Customers with 1996 vehicles will not be refunded for the pcm core charge because we will be doing our 1996 to 1997 conversion to do their pcm, and will not have a use for their 1996 core.
If you already have a 3500 engine installed in your car that was originally equipped for the 3400, all these parts will be able to be used with these other engines as well, although some parts may require adapters to work (like the throttle body). If you have a 3500 engine, we suggest using our 3500 swap kit. We also sell these components individually.