The wheel height difference would be 1", but that's not what you need to know, your looking for tire diameter (overall height of the tire). I don't think there are any 19.5" tires that are 40" tall.
I don't know what the common tire sizes are for the 19.5 rims, you'll need to search that.
The original match for your 7.50x20 would be the 8.25x22.5, (but I don't think they are made anymore) so you'd have to go up to the 9R22.5 which are about 40" tall.
Mike B
