Although its not a difficult job for someone who knows what they are doing, I don't know whey you would bother. Don't believe all the rubbish you read about Crossfires. 99% of this is written by people whop have not owned one and are just perpetuating hearsay.
From a functional point of view, it is essentially the same as the TBI system used on MILLIONS of chevy trucks from about '87-95 and is totally reliable and returns great fuel economy.
Sure the manifold chokes it a bit, but it will easily make up that extra 30hp you mentioned with a mild port job on the manifold and a good tune. A baby hydraulic cam doesn't hurt either ;-)
If you have your heart set on TPI, I'd suggest looking for an '85- car. If you are set on this '84, I'd say you should give it a tune up and drive it for a while before you consider a top end swap.
I've got one, and I love it because its a bit of an oddball and an underdog, and because most people will say they can't make good power..
Its a real DIY car. You can make good power, but its not a matter of opening up a catalog, then your wallet and bolting on some parts. It is not supported by the aftermarket, so you must make most hi-po bits yourself. I dunno what type of guy you are, but thats where the appeal lies for me.
Hope that helps some..
Ben.