I am considering same thing for my M38A1 as well.,. Where and who made the tub must be considered .. Years ago I put an "economy" tub on a CJ7 and right from the start a number of important things did not line up properly. From previously working with aftermarket truck fenders, I expected bolt holes to not be quite right, and there were more than a few including at the fender joints... But those aside, there are a couple inconveniences that have been tolerated ever since, such as the (OEM) windshield frame is no longer in a proper mating line with the (OEM) doors placed on the aftermarket tub (meaning, the front edge of the door seal doesn't hit anything) and the lift hatch gasket no longer seals the "tailgate" area .. The OEM hardtop does not line up 100% correctly with the aftermarket tub because we eventually learned the tub is a couple inches shorter than OEM
... Of course I won't have a "hardtop alignment" problem with my particular M38A1, but still I would be very picky about who made the prospective tub .. There are fiberglass ones and steel ones available out there for the M38A1 .. If you want quality, expect to pay dearly for it