Almost done. I was wondering if putting in a flex fan, and KnN air filter, would be worth the expense for a slightly built, daily driver. I am also wondering how much would a slightly larger ported Exhaust manifold help. They were on the motor not stock . when I bought it .And can I set holes in manifold with larger ports to accomodate smog pipes

Not sure exactly what your trying to do, but the flex fan would give you slightly better gas mileage because it takes less to turn it at higher RPMS, the blades pitch...but an electric fan setup would be even better. I don't like K&N filters I think they're overpriced and don't do what they advertise...they do let larger particles of dirt to pass thru them and into your carb, then your intake and then into your cylinders... maybe I'm overreacting...but if this is your daily driver and you drive thru areas where there's a lot of dust or construction going on...anything your breathing in, your engine is also. This is the part I'm not sure on what your asking, you want to use a least restrictive cast iron manifold...but you need to drill and tap it for the air injection tubes, possibly to gain a couple of horsepower? Take your 305 cast iron manifold and match it with the one you think is least restrictive to see if the bolt hole match up on the last port on either side of the engine and then the angle variation of the exhaust to crossover pipe...you might find that you will have to drill and tap your cylinder head to get the very last bolt to line up and you may also have to make an adjustment of the crossover pipe to line up with the exhaust manifold where they bolt together..I say MAY, but not necessarily. I'm gonna take a guess and say that you got ahold of some truck exhaust manifolds and you wanna use them? All in all I think you'd be better off getting a set of shorty headers with air tubes installed and use them. If you use a least restrictive manifold, but use the same restrictive OEM exhaust system...what's the point? K&N filters look purdy though!

Great information !! I really appreciate the imput, I think I will go with the stock exhaust manifold, for now. I have not been able to ID what the other manifold came off of . Also thanks info on the k+n filters I always wondered if it was just marketing. Not sure about the fan. Thanks again.

hey this helps me to, was thinking bout getting a K&N but not to sure now haha, good answer

I just got a K&N filter on my car with the advice of my car buddy that's been rebuilding, etc car for the last 20-30 years. I don't drive on dirt roads and of course my car is mostly for shows and cruise-in. I myself know nothing about the K&N filter. We all have our own experience. ranago

Honestly Ive never had good luck with the flex fans, run the stock clutch fan and shroud off the 305, they keep my 454 nice and cool, and remember the t-stat temperature selection is important too