Since When Are Timing Covers Not the Same?

Your old red one is a late '68-69 version. There are at least 7 versions of these S.B. covers that I know of. Most will interchange. The silver one you have pictured is a '78 and newer version. It will fit your early engine, but, you will need to remark your timing mark on the balancer, or you will have to round up the passenger side bolt-on pointer to use with your early balancer. The seal hole takes the same seal. It's just the later cover allows you to replace the seal without removing the cover.