lol i bet is you scaled those two cars the difference would be closer to 800lbs or more, 73-74 B-bodies were heavy...70 a bodies were light weight compared to them....now when the 73 340s came out you got the #587 1.88 heads....8.5 to 1 compression,low lift cam etc...the combo of a low compression,low lift cam,small intake valves, restrictive exhaust manifolds(logs),and big heavy car...slowed them down quite a lot...I would consider an engine change, save the # 340/trans, drop in a 360!, you can find rebuildable core motors pretty cheap, drop in some flat top pistons,bigger cam,more torque,you can add 2.02 valves to the 360 heads which after 71 340 and 360 used the same basic heads anyway(915s&587#). a looser converter ie 2400-2800, some more gear,and there ya go.just depends on your budget and what you want to do with the car. I f you decide to build the 340, first thing you want to do is rebuild the con rods and replace the rod bolts/nuts anyway, get some new pistons, rebalance everything, cut the heads for 2.02 valves,you can get some HP by some bowl work below the seats,your trying to increase airflow from the top thru the exhaust.bigger ports,bigger valves,bigger cam,more cyl pressure,more torque to help move along the B-body...headers, loose convertor,more gear,a good combo is important when you go the small block/b-body route.