I went through quite a few gun games, but no Big Top, however
I had played one. If I had your machine, I'd put time into it..
The gun games that I went through, the mechanics come out
to more easily work on. Does any of the side wooden glass moldings
(or the top) have a couple of screws. If so, it probably has a small
lock bar in the back door to release the wooden molding once the
screws are out. If you were closer, I wouldn't mind trading you something
for it, not really because it's worth a whole lot, but just that it's quite
vintage and I don't remember ever owning a Genco gun game.. (T)

I have found that fixing up EM arcades just as enjoyable as EM pins. It is nice to mix it up. I only worked on EM pins until A Sea Raider was basically givin to me. I didn't have a real interest in it at first. Once I started in on it, it was just pure fun, and I now have many EM arcades.
These games are all designed to be maintained and usually come apart fairly easily. Alot of the parts are very similar to pinball machines. With the internet, it seems most parts/scematics/people-who-will- help, can be found on almost anything.
I have no idea of the value, but with EM stuff it seems to always be more a labor of love, than money makers.
I usually spend A LOT less money and time rebuilding EM arcades compared to EM pinballs as there are not as many parts.
Just from the one pic, it looks in great shape, especially the glass.
Looks like a fun project!

I used to have a Genco Rifle Gallery which is of the same vintage.

The entire gun assembly comes off and the entire lower assembly will come out in one piece after disconnecting the wiring too. You should replace the selenium rectifier with a modern Bridge rectifier, and keep an eye on the condition of the connectors. Replace any wires that have dried out with cracking insulation.

It'll be a project, but you'll have a very cool gun game when you're done!

You're on the right track with the glass. Remove the screws & trim and CAREFULLY slide it out so the paint on the backside doesn't get scratched. From my experience, leave the glass alone for now... If something happens to it, you'll probably never find another.

The Rifle Gallery has a different type cabinet front. The coin door was on the right side, and to remove that gun mechanism, you'd open the coin door and remove a wing nut that would enable you to swing it up away from you (it was hinged on the left side). You'd disconnect the wiring, unscrew the hinge and safety chain and the entire works comes off.

Here's a link to Clay's website that has some good information about changing the rectifier and basic EM tips...

http://www.pinrepair.com/em/index1.htm#emparts

Yes, I had/have many machines that the glass came out that way. Most have a lock release
bar inside the cab after the screws are out, but I hadn't noticed one inside your game..
I did have to clean some components in tight spots on some machines, but for the most
part, the component boards were able to come out of the machine..
Like mentioned, if the glass has to rub while sliding out, make sure that it's the front of
the glass. There may be release screws behind the backglass to excess the score reel board
more easily. I would have figured maybe that board had lower hinges, but I didn't notice any..
It'll take time to go through, but she's worth it..

Any chance you guys know what Remington stock was originally used on the Genco rifle games? I have a Davy Crockett that has a cracked stock..... haven't been able to find to much info on what the actual stock model is. It's up and running great, would be nice to have a firm stock in hand. hmmm.....

Model confirmed. Remington 514. Paint on the barrel was so thick you couldn't see there were markings on it. Sand off the black paint and there it is!

IMG_1702 (resized).JPG

IMG_1703 (resized).JPG

I'm also looking for 2 coils for some of the Davy Crockett rifle games I'm getting up and running. The coil is used for the gun recoil effect. The coil has 2 numbers. One is a stock number of 05-2312, the other is a reference number of J-501. They may be identified either way. If you have one, or two, I'd be happy to purchase!