cassette looping electronics help

[Daryl <highhorse@mhorse.com>]

I'm continuing to explore the possibilites of cassette-based looping, using
four-track machines, and I'm thrilled with it thus far.  I've bought a 3rd 
cheap
four-track and am having great fun doing things like moving a loop from one
machine to another, each time recording it at normal speed then bumping it 
up to
double-speed (a perfect octave shift).

There are a few things that a typical four-track won't allow me to do 
though.
Doing sound-on-sound on a particular would be terrific: I'm doing this in a
primitive manner already through modifying cassette cases so the tape never
passes over the erase head.  This yields fantastic, evocative lo-fi 
soundscapes,
but the problem is that I'm unable to hear the track until I punch out of
record.

It seems like there are some pretty electronics-handy folks here (I'm an 
eager
beginner myself, done lots of soldering but no sophisticated mods).  
Anyone have
any ideas?  what I want specifically is:

- to selectively disable the erase function when in record (doesn't have 
to be
per track, just universal)
- to allow monitoring of playback while recording on the same track

I'd also like to extend the range of pitch speed.  Would messing with the 
value
of the pitch pot accomplish this?

Daryl Shawn
highhorse@mhorse.com