Althought the serial number for the 19' Globe Trotter you just bought is a 1964
serial number, based on its 7 panel end caps and numerous other features, the trailer itself appears to be a 1963
or earlier Globe Trotter, so I would not reply solely on the 1964
GT wheel or tire speficications to positively answer your question. The 1961-63 GT wheel and tires specifications might be the same as those for 1964
, or they may not -- I don't know either way -- but I'd depend more on actual measurements from your new trailer than printed specifications for an inapplicable year (1964).
What size tire presently is on the trailer? How does it fit in the wheel well? Can someone with a 1963
GT tell you the offset or backspacing of their spare tire? Can the seller measure the backspacing or offset for one wheel now on your trailer?
One hint: before changing tires, first remove the grease cap from the end of each axle. The grease caps on my 1964 GT axle are threaded on, not pressed on. Whatever the method of grease cap attachment, removing them will give you just enough additional space to squeeze the tire over the axle tip and into the wheel well.
I don't know of the additional 10 mm. in aspect ratio on your used Toyota tires compared to typical GT tires (235 vs. 225) will make the Toyota tires that much more difficult to fit, but it seems the Toyota tires will be wider and fatter than the Airstream tires, making a tight situtation even tighter.