This may help a few to recognize some features of the  different engines.. used in say the mid to late 70's.... like in for instance a 1977 Firebird.. where GM had no less then 5 V8's available.. 

       To mount the different V8 blocks...Different engine mount brackets are used.. as are fewer engine mounts themselves.... but since you can have say a 301  Pontiac or a 305 Chevy in a 77.. plus for some states like California where the greenies mandated emissions leading to the  very strong 403 Oldsmobile as standard over the Pontiac 400 V8.. plus for the manual drivers.. the Chevy 350. All are "correct".

Hope a bit of info here helps down the track.

Below:  Olds V8.. easy recognition sites.. note the fuel pump is on the USA Passenger side.. and this engine has the large oil outlet.. and 180 degree pipe out of the water neck.

BELOW.. Pontiac V8.. note the Timing cover.. and that the FUEL pump is on the USA drivers side.