3/4 " plywood just not PT. You will have a fairly easy transom rebuild and the hardest part will be properly and completely sealing the plywood with resin.
3/4" Marine Plywood-mines 3 sheets glued together with wood screws & bolts been fine since 1994.
paint or sand & stain . back in1994 a 4x8 sheet was $56. the LoneStar has a 1994 115 Evivrude