Sounds simple enough. Thank you.

So so what is the horsepower gain using this roller cam vs the stock 420 cam?

x4 on the 731, its also a good cam if you decide to drop a belt driven intake manifold on it in the future as well.

You should be able to make 500hp +, if the build is right.

Isky 8005 springs or Comp 929's are a good choice. I ran Crane lifters when I used a 731 in my 525SC and had no issues.
Stock valves should be fine.

isky red zone roller lifters

no needle bearings
first question would be how much lift can you run???

On the dyno we seen no difference when swapping from 496 manifolds to Gil with 450 to 550 hp engines. Weight savings yes but if you've already got the 496 manifolds I'd use them. If your using stock rec port heads I honestly woundnt expect to see no more than 435 hp max. Still a reasonable and affordable gain. Also if your going to run dry to the tip there is another proven cam that works well in the 454 to 470 CI range with stock heads however its on a 109 lsa. Don't get me wrong the 731 is definately good choice and proven cam also.

would I gain anything by the other cam with 109isa?

let me ask this on the exhaust.... I can run my manifolds with cooking water, but if I ran my risers dry, would I not risk something getting too hot? I never really thought about running my risers dry. I have a 311 with the swim platform and have no intention of removing. I could easily have water injection to platform. would that work?
Curious of thoughts on that?.

It's a clay smith cam 8800-9-csr. I couldn't say what gain or potentially no gain over the 731 it would have as never did a back to back test on same build. Given your situation I'd stick with the 731. Here is a link you might wanna check out. I'm not certain what you have in mind to build your risers however you do realize they need to be water jacketed correct. The inner pipe just depends on where you want to dump the water. Further back the better but I'd check with some formula guys on just how far back you can go considering the swim platform heat hazard. You might be opening up a can of worms as most have when it comes to build your own. I'd get the correct risers for your application and then you will probably have still some additional work on your transom for proper fit along with possibly some wedges where the riser meets the manifold. Just some thoughts. PM endeavour32. He's been down the same road with fitment etc. If you go to aftermarket heads with raised ports you run into some fitment issues as well.

How are dry headers set-up and how do they work?

thanks for that info. That was helpful as I was not 100 percent clear on “dry exhaust”.

That should not be a problem at all. Can fabricat the the pipe in a pipe. Was originally going to do that.... just may keep the entire pipe jacketed to the end where the pipe dumps to the transom.