What octane and what timing needed

Hawk 540 cid BBC v8s
9.0:1 compression
Dominator carb
Wieand team g intake manifolds
World products Merlin 1043C Grumpy Jenkins 320cc heads
Crane gold race 1.7 rockers
Summit 1797 flat tapper hydro camshaft 228/228 .544/.544 112 lsa
Stainless marine performance exhaust manifolds and 4" tailpipes

Could timing be pulled back for 87 octane or. What total advance.

9.0:1 with cast iron heads I would run 91 to be safe. I would run between 32 and 34 total and look at the timing mark on the ground strap and adjust accordingly.

Thanks.

The old Owner had ac delco mr43t spark plugs. How wrong is that plug and heat range for a 550-625 hp engine

Blackmagic94 said:

The old Owner had ac delco mr43t spark plugs. How wrong is that plug and heat range for a 550-625 hp engine

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It's a throw away plug in my opinion. It is the plug that comes standard in all the Mercruiser engines (that use that size plug). It is a 6 heat range and a non projected tip plug. Same as an NGK BR6FS. I use projected tip plugs because the tend to burn a little cleaner. In a cast iron head, assuming the tune is correct, I would start with an NGK R5674-7 and take some readings from there. Gap will be determined by the type of ignition you are running.