To elaborate… others have run these manifolds without issue on HP 500 and 500 EFI engines. Those combinations have about 14 degrees more overlap than yours. The HP 500 was prone to a little bit of reversion with the factory exhaust.

For peace of mind, you could get IMCO to custom fit the riser as stated earlier. More drop never hurts.

I did ask them about making risers or if they offered anything else but said what they had on website was it. 🤷‍♂️

I’d just run’em.

if overlap is what you look at then what’s the limit to that before you start worrying about reversion?

Part of me says “run’em” and part of me says don’t do it. That’s the financial part of me. These dang big blocks are expensive.
I’m gonna break the cam in on a stand because I have to install the inner valve springs after the break in. That gives me a good time to retorque my head gasket and also check for water in manifolds. But if there is water I’m out the cost of the standard riser then on to something custom. If I can get them to make them.

What is your old screen name?? It may have a different email address attached to it than you currently use.

BTW, I do not think you will have any issues with reversion with that cam.

That’s one of my issues with the old log in. I don’t even remember my screen name it’s been so long ago. OSO already had my email address on file so I had to use my work email to register this time.

I don’t have any way to search by email address. I can search by an IP address or even a partial screen name. Send me a PM with your IP and possible screen names if you’d like me to try and find it