Old 396 help

Long story short I have been trying for years to get this old engine out of a neighbors building and today we finally got it out. Trust me it was buried. It was kept well covered and oiled up and the crank turns by hand. I am trying to find out out exactly what I have. I have several questions first the oil pan (pic attached) did it come this way with the welds at the bottom.
The block number is 3969854 and the heads are 3964291. Are the heads original to the block
The head has a marking of F 3 with either a 8 or 9 with Hi Perf

There is a 5T on the block and GM4T on the head

I have seen valve springs but these seem to have a extra band inside (pic attached) what is that?

Any thoughts on what I have here would be great. My plan is to put it in my 76 Corvette [ATTACH][ATTACH][ATTACH]Attachment 74739[/ATTACH][/ATTACH][/ATTACH]