Lonnie,
just finished installing a Chevy Duty headliner on my 50....mine was too long, I had to trim a little off mine to make it fit.
late 49 and 50 should be the same...does yours have the "floating" center strip?
I put rear section up first with the center strip on it. then worked the front section on. it was definitly a two person job and we had to take several frustration breaks....finished product sure looks better...glad I did it. have you considered the new one-piece ABS headliners they are now selling?
Chuck