There is one solution in the post immediately above yours. Personally I keep an assortment of gaskets on hand and pick the one that produces the best level of date magnification as the first priority with crystal sitting height as a close second goal.
Which crystal gasket should I use?
Crystal gasket shave - DIY
I have had the best luck using a 2.7mm gasket with the gen crystal. Seems to have the most accurate date magnification to me.I'm in the same situation. I have a Pepsi CF GMT V3 and got myself a gen crystal. I took it to a watch maker who told me it won't fit. I didn't ask him if he tried the CF gasket or the gen one (not sure the gasket was in the package, but I think so).
If I understand your other post correctly, I should find a 3.1 mm or a 2.85mm gasket for the gen crystal?
I have had the best luck using a 2.7mm gasket with the gen crystal. Seems to have the most accurate date magnification to me.