Douglas,
I have done a big build up on my I6 and it has been pretty expensive to do. I'm still not done with it either

. Something I would like to see is what can be done with an inline six car that will make it perform better all around. Something that can be done on a budget and be very fun to drive. I will give you an example of what I mean. When I was shopping for a car to be my daily driver I whittled it down to two choices an SVT Focus or a Neon SRT 4. While the SRT4 was the faster car, the SVT F was by far more fun to drive. So I picked the SVT Focus. I have raced it in the 1/4 mile very often and many SRT 4's have put me to shame. On the street and at the autocross course it has been a different story, the SVT F was by far superior. While big HP numbers can mean great time slips at the drag strip, it does not mean you are going to have fun with it. This is how I feel about my 67 Mustang with 200 I6, I have been building the motor to it's max potential and it has cost me alot of money, but the gratification of people when the see my car and what is in the engine bay is priceless. Here is what I have in the car so far:
custom forged pistons, with rings and bearings from Ross Racing $700
Hooker Header $350
Weber 38 2 barrel carb with adapter $400
ARP head bolts $75
Corteco gasket kit $55
Hipo balancer $215
7 qt oil pan $245
274 cam $145
lifters $55
Roller Tipped Rockers $415
Push Rods $45
Valve Springs $80
Dual Roller timing Chain $99
odds and ends $200
Machine Work $500
Now for my future project that I have already purchased parts:
Offenhauser 3x1 manifold $240
3 autolite 1100 carbs, well I already had 2, so 1 carb $140
Eaton M90 with intercooler and bypass valve off of Ebay $320
The look on peoples faces when they see that it is a 6: PRICELESS
I encourage you to keep on with the I6.