Well, in that case! lol

Seriously though. Silent choice exhaust is going to limit the camshaft you are going to be able to go with. My personal opinion, is forget silent choice y flappers. We have plenty of sound solutions that can reduce noise, without the reversion issues of silent choice flappers.

The GM heads are going to limit your potential. I'm not even going to touch base on cylinder head talk, as I do not want to wake the bears.

Get in touch with bob madera (rmbuilder on the site) and develope a game plan.
Discuss your goals, budget and the parts you currently have.

After you have the recipe, develope a relationship with an engine builder / machinist local to you.

I'd try to use an aftermarket aluminum head if Your budget allows.
I'd have a custom cam specified by Bob and buy the valvetrain components from him too.
I wouldn't use anything MSD. Use a magnetic breakerless distributor in good mechanical condition and a Daytona sensors CD box and coil.
I'd scrap the silent choice.

I think the key to success in engine building is in the planing
by this i mean finalize your real objectives timeframe/hp/tq/rpm/duty cycle and of course budget. And stick with the plan.
In regards to budget this is king. (you can build anything if budget is no issue)
once you think you know what it will cost, double that number, now you are getting close. Take that original budget number and keep that much in reserve, i bet you will need it.
Many used quality parts are available here on the swap shop but time is required to find the right parts that work together to fit your objectives. Hodge podge performance parts buying gets expensive if they do not work together or changes in plans.
In reality most would be better off purchasing a good running swap out motor complete and rigged for a fixed price. Many here on oso all the time. Now you have your motor as a working spare. Mid season ship happens.
Just my .02 with .01 change
lots of luck and don’t be discouraged by the esoteric nay sayers.

Everybody's going to have an opinion on engine build none of are bad
Get yourself a good machine shop and a parts guy take it from there you could always come back and ask questions The only thing you have to consider is how you going to use this engine

Mercury racing made a couple engines, that you can look at for reference.

454 420HP engine.

This engine was

8.8:1 compression

GM rectangle port iron heads that received 2.25" intake valves and a custom valve job. The 365HP 454 mag used the same head, but had 2.19 valves, heads were as supplied from GM.

228/236 flat tappet camshaft, 530/551 lift 114LSA. Crane #132561 camshaft.

Roller rocker arms, 800CFM holley carb.

They also made a 440HP cyclone engine, which was the same as the above, however, it had a bit more aggressive camshaft. That camshaft was 231/239 110LSA with 550/558 lift. Also flat tappet.

Then there was the HP450 engine. This was a roller cam engine. This engine had a crane 169611 camshaft. 222/230 110LSA, with .576/.598 lift. Also got the GM rectangle ports with 2.25 intake valves, a single plane dart intake, and 830 Holley carb....8.8:1 compression.

Now, keep in mind, these 3 engines listed were all designed for a max rpm of around 5200RPM and run on 87 octane. If you are willing to spin the engines to say 5500-5800RPM, a little more camshaft, and a little more compression, and 500HP should not be a problem, even with those GM heads. Going to a set of aftermarket aluminum heads that are sized properly, with the right cam/compression combo, 93 octane, 575-600HP is within reach.

What's wrong with MSD?

I think I'm going to retire the silent choice. I would like a nice header style exhaust.

They die on a regular basis. Some people have great luck with no issues for years. Some others go through multiple boxes in a season. Other boxes have a lot more options for the same money or a little more.

What would be a good head? I was told the .088 heads would flow better then the pro comp 320 115 runners.

Here's a couple pics of what the distributors are known to do. Had it happen to me with a garage kept, 1 year old distributor:



Add to that, the fact that their CD boxes are well known to fail without warning.

Been there, no going again!