i'd stick with the Y7 block and slap on the y8 head. Just make sure you remove the oil passage plug from the y7 block. I've done a few swaps like this myself with a greddy bolt on kit
your car should start ok with the p2p ex ecu, but its best to run a ls obd2b ecu cause of the different fuel maps or you can also run a obd2-obd1 conversion harness with a chipped ecu so you can tune it in the future.