"62500 *32bits. The flash is possible?" about 190 kBytes, yes it is.

If you want to stay with the '51 series, use a Philips MX, it has .. is it 22 or 24 bit addressing without bankswitching.
Last I did volumetric measurements, I used the Philips XA, 1 to 16 MB addressing, 2 UARTs and 32 bit multiply/divide it worked quite nicely. Actually, I used 3, one for PCI bus interface, one for stepper motor control (to 60 kHz) and one for volume, all interfaced with DPMs.

Have fun,

Erik