So I recently built a 2.3l stroker and found out that the block is actually a JDM 7 block. The car was just started for the first time and started to overheat at idle. It has a half rad w/fan, all evo 8 cooling components and everything is hooked up properly. No air bubbles, fan works, thermostat was checked, water pump is moving water. I was told the water pipes are slightly different for the evo 7, so my question is what modifications or differences are there to get the evo 8 head to the evo 7 block and make all the cooling components work.

you are looking in the wrong spot. there are no compatibility problems that would cause your issue.

Are you primarily looking at the gauge cluster temp indicator or have you checked the reading from the temp sensor?

The temp reading was from the aem infinity

Update, stopped by the shop and since they are slacking peeked into the rad. looked like a little bit of oil in coolant. Can the head gasket really be bad being a brand new decked, block, built head, new head studs and new head gasket (OEM).

no. if its the shop who did the work telling you head gasket is bad they are just trying to get you to pay for their mistake. a fresh rebuilt shouldnt be overheating without an error made on the mechanics side.