[Pampered-Z]

You really want to start with determining how good the shortblock is. Even with good oil pressure that's not telling you the condition of the rings and cyclinder walls. Normally if you know the engine has been taken care of you sould be fine with an engine under 100K, but if your not the original owner and the history is unknown you are going to want to at least be ready to freshen up the bottom end, rings, bearings, upgrade bolts and oil pump. You could at least do a leak down test.

Don't assume oil pressure means the rings are going to handle the extra cyclinder pressure a heads/cam is going to add, or that the bearings are good enough for the extra RPMs you'll need to spin the engine to make that 400HP number ( if you really want 400HPs). That's a bit more then doing something like a 305 cam, 400HPs is going to need a 306 or better cam, that means spinning over 6500 RPMs.

Also as a reminder check your budget, rebuilding a LT1 is going to cost more then your standard SBC. Gaskets, timing chain sets, hardened pushrods, etc all needed. 400HP can be on the edge of the stock fuel pump and injectors as well. So make sure you plan this out. Nothing worst then running out of dollars in the middle of a project.