Gonna have to scrap the whole LS1 setup for 1K-1.2Krwhp; no way in hell you will keep the heads down. Gonna have to spend the big coin on an LSX block and heads. Your LS1 block only 4 bolts/cyl to hold the heads down. The 7-800 is very do-able, and quite do-able without needing sleeves or a stroker crank.