You may be able to do this with half of the receiver. If you bridged it for 140 watts, it may go up in smoke. Only certain amps can do this, and must be designed to. You might be able to use both halves separately. In other words, two 70 watt amps.
Receiver monoblocs
I have two Marantz 2270 receivers which have preamp out/ power amp in jumpers so each section can be used independently. My question is, can the stereo amp section of each receiver be used in monobloc fashion so I would have essentially two 140 watt monobloc amps. Or is it not that simple...