Oh. I'd change the oil sump gasket and the valve cover gasket. Make sure to get some LocTite 518 Gasket Eliminator (best) or RTV Black (OK,) and get a batch of SBChevvy valve cover studs - for cast covers for up top, and for stamped covers for down below. The studs are helpful for locating the gasket and cover while you're tacking things up - and I find they help. Both the valve cover bolts and oil sump rail bolts are threaded 1/4"-20, so SBChevvy studs will work nicely.
If you haven't gotten the later one-piece oil sump gasket, do so. The older 4-part gasket is a pain to deal with if you don't have practise (although the studs will help.) Daub a little extra sealant in the corners - you'll see where I'm talking about.
Have a low-value torque wrench, and USE IT! As I recall, oil sump and valve cover bolts are torqued to 8 pound-feet - about 64 pound-inches - and overtightening these WILL crush the gasket and you'll end up doing the job again! Don't ask how I know...
Another little tip - once you've got everything down to "contact," go for a sandwich and a cuppa - about 15-20 minutes' break. THEN, come back and torque everything together once you've gotten a "skin" on the sealant and the sealant won't squidge out anymore. Take your time here, you don't need to do this again.
Any questions? You'll find that the rest of the gaskets seal air, or water, or both - BUT NOT OIL - and you won't need to change them straight away.
5-90