For owners that DON'T track their cars much, plexiglas has been used for decades without problems. I know of one street GT-5 in Nor-Cal with a cage with roll bars going thru it, that has used plexiglas since the mid-'70s. It even passed CA visuals for smog tests at one time!
But when all this work is done, I doubt if a removeable window will help engine maintenance. There just isn't that much you can reach through the opening. A quick-release upholstery bubble conversion, slotting the seat-back straps so the seatbacks fold down, removing both rear quarter window glasses, and one of Johnny Woods maintenance platforms that sits on the ZF is all that's necessary for routine maintenance. Beyond that, the engine comes out.
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