I'd definitely re-pin my TBI harness if I was in your position! Its really not that tough, and will save you a lot of money. Most of the wires that the TPI needs have already been run for the TBI. Only just a few would need to be added, or changed, and those that need to be removed can just be cut so they are no longer in view. Some TPI connectors are slightly different, but it is very easy to un-pin the TBI connectors, and swap them over to a TPI connector. Same with re-pinning the ECM for the `165 ECM if you are going MAF, just use a paper clip, and you can easily re-pin everything. Biggest thing to do is download an ECM pinout for both your current ECM, and the new ECM, and make sure that you keep track of all the wires. Some of the TBI wires will be different colors than the TPI wires, but if you make sure to lable every single wire with a peice of masking tape with their original designation written on them, then its very easy to keep track of them, and make sure that everything gets hooked up correctly.
I did the TPI swap in my truck, and as far as the work goes, its been pretty easy, and thats starting with a truck that was originally carburated! The only issue has been getting nickled and dimed to death on little things that the setup has needed, and the amount of time it has taken me to rebuild my truck to a position that I could start it.
I am now facing a pretty huge vac leak off my runner to intake connections, so make sure you don't make the same mistake as me, and put the gaskets on the ride side of the intake the first time around!
If your engine is bone stock, you should be just fine running the stock TPI chip with the stock TBI engine, should mostly be a bolt the TPI on, re-route your fuel lines to the fuel rail, and do some electrical type swap.
If you plan on modifying the engine at all, start off with a MAF system, then convert over to speed density once you have done all your modifications and have got the chip tuned as well as you want it, MAF is far more leniant with cams than a speed density setup. However, once you've got things figured out, do yourself a favour and swap over to speed density. You can then ditch the MAF, which is a bit of a bottle neck, and clean up your engine compartment by running a cone filter on the throttle body rather than having a bunch of ducting all over the place.
If you plan to run the stock TBI engine, then start off with a stock speed density system as it is a bit more efficient, and is better programmed as it is newer than the old MAF systems.
