OP. Good idea to check for clearance regardless. Just gave you an example of what can happen when installing aftermarket performance heads, then usually leads to larger valves, possibly bump the compression. That alone is enough to check as the stock 365 mag Pistons don't have much intake valve relief. What causes the biggest issue with p2v clearance is if you did by chance advance your cam which changes your valve timing and decrease the int clearance and increase the exh. Not a big deal here just thought I'd give you some advice if you haven't run across it before.

I will pass the info along to my mechanic. I know the heads are dart pro 1 that's pretty much it.

Usually reversion is caused from too much overlap. As duration numbers get higher, so does overlap. As lobe separation gets narrower/tighter, theres more overlap for a given duration.

A cam with a 114 LSA, can have more overlap , than a 112 LSA, depending on the duration.

Combustion chamber design, can induce exhaust flow reversion as well .

And of course, exhaust manifold design.

My buddy ran crane 236/245 114 LSA cams in his 454s, with stock crappy merc iron center rise manifolds that came on 454/502 mags, for over 10 years , without any reversion. I was surprised when we took the cams out, that they were that big. On oso, that combo would have meant immediate water reversion. He has since went to stellings and dry tails, but prior to that, never had a reversion issue.

So what would be the most "cost effective" manifolds to go with?

Offshore777 has a nice set of Gils with long tails for sale in the swap shop. They look like new and he only wants $1100 for a set of them. Depending on the specs of your cam you should be fine with them. Are Gils the best? No! Are they bad? No! For what you are building they will work just fine.

Man that would be great!

I'll text him in the morning... Thanks

Stainless Marine. Buy them once and then you don't have to pay for a second engine.

Well I may have too, I may lose out in these Gil's for sale!

Like black baja said look for a set of stainless marine manifolds and risers. There are a few sets for sale as of recent. I saw some on Craigslist and eBay by accident also. Never hear any issues with cracks and ruining an engine with them. Gil's are fine but always risk for cracks and the stainless marines will give you same performance.

Do the stainless marine manifolds allow for the risers to be rotated inward to help with spacing issues? I know the Gil risers bolt to the manifold with 4 bolts, so they are pretty much fixed in one orientation unless you cut and reweld the flange. Seems like I recall that the SM's use some kind of collar to attach the riser.