All the Chevy Small/Big Blocks have same bolt pattern, even today's trucks are same. Two things probly needed are the two feet on it to bolt to crossmember there, unless that has been removed and the depth of case. Probly whole rig is from a big truck, there was no 454 back then, but did have small blocks. Some big trucks had really huge flywheels and used an adapter between engine and bellhousing. One of those things you will have to look and see what was used I guess. OR, did they use a "footless" bellhousing and not bolt it to a crossmember?? The housing should have a GM number cast into it somewhere once you clean it up and might help. Is it older cast iron or newer aluminum?? If you hold up trans, you can just unbolt it from housing and take off linkages to pull whole engine and clutch as one piece. Best to remove some front tin or whole front saddle to get good clearance and not have to lif so high. Most times the saddle comes off with rad support bolts and back at the body where tin bolts on. A few wires removed and set aside and whole front lifts off in one piece.
