The R12 compressor can fit (I've done 3 myself) if you drain the R12- compatible oil into a measuring jar and then replace it with the same amount of R134 ester oil. There is one type that is specific for this conversion.
I prefer the R12 cpmpressor because it has both high side and low side valves on the back and you can check both pressures with the gauges. The r134 only has a low side (or none at all). I put on a 90 degree conversion valve on the high side valve of the compressor ($15 for the valve). That way you can more accurely gauge the pressures and how much R134 to add.
Happy cooling.
(A/C is important here in south Texas,also).
el Raidman