100% agree. My advice was only intended if you are set on building something but if the mag is all good just run it and have fun.

Haha , Save money ? Point made ! I bought my house almost a year ago , for closed , everything needs attention ! But I moved here BC I'm 10 minutes away from my favorite body of water. That boat is going to be on it this year ! I feel like I won't be happy without going roller ! Any suggestions on what to use ? Also , I know everyone says to throw away the stock exhaust ! They put these manifolds stock on 502's , what will these manifolds be ok to use up to , about 450hp ? I certainly won't be able to do exhaust this year also.

Go with the Mag and a roller cam. What exhaust do you have? If you have the factory Merc exhaust you won't be able to run a big enough cam to get 500HP out of the Mag due to water reversion. You will only get around 400HP with a cam suited for the factory Merc exhaust. I was also on a budget with my build. I didn't have the money to build the new engine and buy performance exhaust. I got 407HP out of my engine ran it for 2 years with factory Merc exhaust with no reversion problems. I have had Gil exhaust the last 2 years but it runs so good I don't want to bother putting a bigger cam in it.

So , I talked to the builder. He says , well u should think about a cam upgrade now, there are much better grinds then what can in the motor. I agree with this , so then the questions came with what route to take with this cam. I really can't see taking this motor further then na for this boat. But I'd like to do it right the first time and save money in the long run. Is it worth me asking a guy I've read about , Bob Madura for a custom grind ? Or is this considerable more cost ?

Decide what exhaust you are going to run before you pick your cam. Yes Bob is the man and worth every penny! I'm going to use him for my next build.

It's better to take a year off than it is to face many years of misery.

IE: better to do it the way you want and should vs making bad choices in order to get on the water earlier.

Just sayin.

I'm running the Isky 270/280 Mega hydraulic cam with Scorpion Racing 1/7 roller rockers. I made 407HP on the dyno. I had no reversion problems with factory Merc manifolds. I think that is about as big as you can get with factory manifolds. I'm sure Bob can grind you something similar in a roller and you might get a few more HP.

http://www.flatlanderracing.com/iskycamsmarine.html

put the mag in stock, enjoy the summer. keep your eyes open for used exhaust, intake etc on here and FB. once you have collected some parts, exhaust, intake/carb then you can work with Bob or somebody and match a cam to what you have and maximize your gains.

This is a marine engine, you are going to ask it to work hard in an inhospitable environment, It needs to be built right with the right parts, It is not a 74 camaro with pep boys dodads and 99.95 black jack headers with cherrybombs. If it goes boom, you dont just coast over to the side of the road, you could very well be stuck in the middle of lake michigan in very ugly conditions,

You CAN build a 500 hp 454 easily and fairly economically too but it has to be done RIGHT or you will get disillusioned at spending 3 times what you needed to while sitting on the dock because your chit is broke You currently do not have the dollars or knowledge to do it right. No disrespect intended, its just the way it is, we have all been there,

Put it together with a stock mag, should still get you low 60's which isnt bad, While you are enjoying it figure out exactly what you want and how to get it.

Yup. Don't do an aggressive roller cam until you can get better exhaust at the same time.

Thanks to all for your sincere advice! I have taken note of several good points. My builder is very knowledgeable and has been great with it all. He's building 25k motors for guys who probably are less hassle then me ! Lol. What is , when I first called him, he mentioned a mag motor that was very fresh a guy had sunk , turned it in for a core . Builder said he'd sell for a good deal all gone through , intake to oil pump. So , I wrote a check to get it all going. I'm excited and want to make the right steps at the right time. Getting advice , helps me see the ( big picture ) as I go through the process . Thanks to all , I would appreciate any further comments.