Inverted flying cub

Are there any Ok cubs with plastic mounted tanks that will fly inverted and if so are any of them worth trying?
Only reason I ask is cause of the price most cubs are 15 to 25 bucks compared to a decent black widow price that's a steal. Another thing are parts and glow plugs available for them at fair prices or is it just better to bite the bullet and get another black widow. Thanks PeteJ

Personally, I would go with using a Cox engine over the OK. I never liked the OK engines until about 10 years ago. I then discovered them to be very interesting. My use for them however is mainly for free flight. The engines themselves are quite under powered compared to a Cox . Just as a example, the OK .074 offers generally the same power as a Cox .049 Babe Bee.  But, Ok made so many different versions of these engines, I discover new or different styles with regular frequency. The OK could probably made to vent just like one would do with a Babe Bee. This would be to place a piece of fuel tubing on one nipple, run it all the way around the circumference of the tank to the opposing nipple. The issue is getting small enough tubing to retain itself to the nipples. I usually CA the tubing onto nipples when this is required. It's not permanent and can be cleaned off if needed.  Cut a v notch in the tubing on the underside of the tubing opposing the fuel fillers. This would allow for venting upright and inverted.

                   I personally would opt for using a OK .049 B and do away with the plastic OK .049 A tank. One could still use the OK.049 A but you have to drill out the threaded holes in the radial portion of the case and use this for installing screws to attach to firewall. In doing so, the engine would no longer be able to use the threaded holes which retain the tank.  This would enable the use of a remote  tank.

          A Cox or OK using integral type tanks is going to offer complications in engine run not too mention short duration. A proper tank will circumvent both of these issues. A Cox Black Widow is not without issue even inverted. It eventually fails to feed and the engine goes lean and could possibly quit. I've developed many ways to solve these problems but they exist and one needs to have a lot of patience with them. These problems can be virtually eliminated if you use a remote tank.

        If dependability is what you seek, OK engines in my opinion are not the place to look. Not that I'm opposed to them, it's just that quality control was all over the place. Especially the versions offered in the 90's which were built from whatever parts were laying around.

      As for your glow plug comment. Glow plug availability has diminished over the past 5 years. While a OK can utilize a standard glow plug, these too are becoming increasingly expensive. Not as expensive as a Cox plug but they're 3-4 times more expensive than what they were. The OK .049's utilize short plugs, these are becoming harder to source as they're just not commonplace any longer. The good thing is that OK engines are a low performance engine and Fireball glow plugs still manufacture short plugs which are probably the least expensive plug you can source today.

        The last of the OK engines used the same  cylinder head thread as a Cox engine which could now use a Cox glow head vs a glow plug and adapter. 1/2A engine performance is completely downgraded when you use a standard glow plug like the OK does. This is the reasoning for the glow head vs the glow plug. The choice of engine is totally up to the user.