Same as 14 years ago.  Don't.

If a seized compressor is your goal, yes.
FWIW, "evacuation" is the process of pulling a deep vacuum on the
AC system facilitating the removal of any moisture that may be
trapped inside.
Your description of the system performance suggests that there
may still be a viable quantity of R-12 remaining in the system.
The removal of this remaining quantity of R-12 is called
"recovery."  Recovery always occurs before any attempts are made
at evacuation.

Controversy?
R-134a doesn't carry mineral oil very well, the lack of
lubrication results in a seized compressor and a contaminated
system.
Ester oil is carried fairly well by R-134a and co-exists fairly
well with mineral oil but it is not the ideal lubricant and the
added volume along -with- the existing mineral oil results in a
loss of cooling efficiency.
PAG oil of the proper viscosity is always the better choice,
however, it does NOT co-exist well with mineral oil necessitating
the complete removal of the mineral oil from the system before
the installation of PAG oil.

May not be a refrigerant problem at all.  I'd look first at
airflow across the condenser.  Is the condenser clean or is it
plugged up with debris and bug carcasses? Have you measured the
delta temperature between the condenser inlet and outlet?
Does cooling at idle improve if the condenser is sprayed with
water?  Is the fan clutch working as it should?

buy sum redtek

 You can't mix, it's one or the other - they operate at different
pressure ranges (R-134a much higher) and require different compressor
oils/  Put R-134a in an R-12 system and bad things happen to the
mineral oil in the compressor, it needs to be flushed and changed to a
synthetic PAG or POE oil.

 If you want to change over to R-134a they have kits with the
replacement seals for the compressor and adapters for the fill ports.
But it is a rather involved process - you have to evacuate the system,
take out the compressor to drain the oil and change all the seals,
then flush out the evaporator and condenser cores and all the lines
with solvent.  Some cars you need to replace the cores because they
aren't large enough or won't take the pressures.  Some cars you need
to change the metering orifice or the TXV.  Mount the new compressor
and fill it with the right oil.   Then you have to test the oil to
make sure you have the mineral oil residual down to an acceptable
level around 1% max.  Install a new filter-drier, evacuate and leak
test, then evacuate and charge with R-134a.

 But that's a long drawn out pain in the keester, so...

 If the system passes a leak check and is leak-tight (or as tight as
a car system can get, meaning it leaks down after 6 years or more)
just get it recharged with R-12 and be done with it, it is still
readily available.  You pay more for the refrigerant, but you save all
the time and expense of doing the conversion so it's a wash.  

 And by the time it needs recharging again the car will either be
ready for the scrap heap and it won't matter, or ready for a proper
restoration and you'll spend the money.

    --<< Bruce >>--