Are you setting the timing with the SPOUT connector pulled
as it should be?  The observation that the timing is jumping
around a bit is typical of setting the timing with the SPOUT
connector installed.  You may want to thoroughly clean the
MAF sensor if it has one to make sure it is reading the air
intake correctly.  I don't recall immediately whether the
'95 460 was MAF or speed density but, I believe it was MAF
controlled.  There are instructions with photos in various
places on the web.  You may want to make sure you have the
correct brand and heat range spark plugs installed.  Many
times, a plug of a different brand with the same heat range
rating may actually operate in a different heat range than
the same heat range designation of the recommended brand.
Have you checked to make sure the engine is not running a
bit on the feverish side.  An increase of only 10 deg F or
so above the recommended operating temp can easily cause
this.  An incorrect EGR flow will also cause this.  You may
want to replace the EGR control sensor.  I don't know if
yours has an EVP sensor or a DPF sensor.   They do not
always set a code.  Also, pay close attention to the routing
of the spark plug wires.  Incorrect routing can sometimes
result in crossfire under load.  It is possible that a
crossfire to another cylinder just stating the compression
stroke can be the same a super advanced timing causing
extreme pressures in the affected cylinders.  The factory
shop manual and some others will show a specific way in
which the wires are to laid out and installed.  This can be
a PITA but, may be well worthy the effort.  There have been
TSB's to this effect over the years related to some Ford
engines.  Don't specifically recall that being the case with
the 460.

Good Luck
Lugnut