Newbie needing help to ID what BBC configuration this is

Bought a 1975 Covette a few years ago, and do to health and surgeries I have been unable to tackle it. Now I am ready to dig in and get it on the road. My problem is I have no idea what the configuration is. Here are a few of the details:
BBC Block ID 3999289, 454 date code I believe is 125 73? - Aluminum Intake manifold 3933198 - 800CFM Holley Dbl.Pumper no choke horn - Head ID 3919840 date code J22 8 - M22 Rock Crusher 4 spd - Tunnel was modified to receive a Hone a Drive but has been removed - no emergency brake I believe because of the hone a drive - Hooker chrome headers and sidepipes - Autolite M66 spark plugs - The car was housed in Canonsburg, Pa. for over thirty years with no use other than yearly maintenance because the son died a year after he had this modified. The mother has no records, but kept it garaged in memory of him until I purchased it. She stated she thought it was modified by Yenko, but I thought he was not doing cars anymore after 1970 or so.

I have looked up all the ID's and non of them match up with a 454 because of the port configuration, except the LS6 from I believe is a 1970. Hopefully someone has some knowledge that they can fill me in on what this configuration is. Thanks in advance!

the 289 block is a easy to find. i have some built them in 427 and 454 , and bigger 510 but i would not think its that big . if its is what you say as to time frame. 840 heads i used on 427 to 540 cid. hard to tell what you really have 427 or 454. i can tell by looking at it. as gm 427 was internal balance but back in the 70s i know many that built the 427 over 454 if you want to know what rods and othere parts all gm race parts? you have to pull it or drop the oil pan . if run good i would just drive it .seen many engines built with 289 block and 840 head s that Gm never built

bbc castlng id #3999289 454 72-79