I sold 2 3963512 blocks on EBAY in the last 6 months. One was a L-19-9 dated (December 1969) 2 bolt main LS-5 454. It was .030 over and had damage from a roller lifter breaking...I got $987 for that one.
The other was a December 18 1968 block..It was a 4 bolt main 427. It was bored .060 over, had one hole that needed a sleeve. I got $850.00 for that one. It is ALL about the date codes. If you find a guy that has a car that needs that block then it is worth whatever he is willing to pay.