Heater Core Removal Question

[z3beemer]

Just finished a 3 year resto Mod project on a 69 mustang coupe. Even though I thought I'd be proactive and replaced the heater core while the interior was out, yesterday I had it out on its first shakedown run and discovered an antifreeze leak on the passenger side. The hose are tight and dry so it must be leaking inside the box. I know its a pain in the a** to remove it without tearing most the dash apart so has anyone ever tried this or know if it will work? I though about using a cut off wheel and making 2 vertical cuts in the front half of the heater box on either side of the core, remove the clips that hold the front and rear halves of the box together, remove the front of the box, replace the core, reinstall the front have of the box and seal the cut lines with black RTV. Any thoughts if this will work or if i"m overlooking anything?

Thanks
Paul