heater core coolant leak?

i have a 1991 supra with the 7mge and auto trans. everything is stock. i bought the car with a locked up motor. i bought a new long block and had to swap everything off the old one to the new one, like mounts, fuel filter and front brackets. the car runs and drives great now but after driving it for a while you start to smell antifreeze in the cabin. when i parked the car i noticed a puddle of coolant under the car. it seems to be coming out of one of the main frame rails that go from the front of the car to the back (where the body plugs are located at). i drove it a couple days and found that if i don't let the revs get above 3 grand i don't smeel coolant and i don't have a leak. driving about 15 minutes and only revving it once above 3 grand then you have the smell and the leak. you woudl think it's the heater core with a leak in a fin blowing through the vents but the heater core is on the right side of the vehicle and the leak is on the left side ??? short of ripping the front interior and dash out and looking for the leak, what are some easy things to check first? i'd really appreciate any help. thanks.

In ur local car stores you might want to start with buying somthing like selleys high pressure selent stuff for the heater core and also if you look at the rubber pipping in the back of the engine they can be weak you willwant to take that of and one way or another buy a new pip or cut it were it has split if it at the water jacket part and that way it is new rubber to chew through which takes ages also... Otherwise after that you could be in the motion of blowing a head gasket which you ned to get a bottle of water tip it upside down while running over the radiator and if bubbles you have blowen a head gasket unfortunitly.. Let me no how ya get on and all the best