If you are going to be 360 and make 600 real HP you are going to need some RPM. 7k at least and 7500 would be better.
That said, your ring seal will suck. You’ll need to run 1970’s bearing clearances because the main bores will move around like crazy.
At that compression ratio with those thin decks getting the head gaskets sealed will be problematic at best.
At 7500 you’ll need a GOOD oil pan with a big pick up tube. Not an OE sized tube. You’ll need full groove mains so the rods are getting oil all the time. A HV is mandatory.
I would NOT use a 4 bolt cap on that block. If you have not drilled the outer holes then don’t. If you have you have made the weak block considerably weaker. Cap bearing area isn’t your problem. That thin, flexible block is. No cap/bolt arrangement will fix that.
Hard block can help, but it’s a bandaid at best. It will stabilize the bottom of the bores, but it won’t make the main webs any stronger.
And save your money and skip the girdle. It adds weight and shifts the loads to the wrong areas.
You are asking a mass produced engine block to double its engineered RPM (most of these engines never say the high side of 4k and if they did they weren’t making any power and they weren’t at 4k very long) and double the power. At least.
At a measured 13:1 and with those heads I’m not sure how hard it’s going to be to not make way more than 600 HP. Then you‘ll either live with more power or start detuning to get the power down. Neither is a good option be detuning is contrary to my nature.
You are trying to save money and time. But you won’t. It will cost far, FAR more to cobble that stock block together and try and keep it alive, and when it ***** itself either build another stock block that will soon **** itself (more money spent) or then you’ll spend the money to buy a block.
Spend once, cry once. What you are doing is setting yourself up to fail.
