Please help identify this engine

I would like to put it on an small airboat.

For an airboat your best choice for a tank would probably be to pick up a 5cc tank mount conversion, such as that off a Babe Bee.  They cost a bit more, but make the set-up a whole lot simpler.

http://coxengines.ca/5cc-fuel-tank-conversion-for-cox-049-engine.html

Also, if your glow-head works ok you should not need to get anything else to get it running.  Spring starter is handy but not essential.  What you need to consider is what direction you want the engine to run.  It will run equally well in either direction, so if you use a starter spring it will have to be chosen in relation to the direction of rotation.  On an airboat I would assume you will be using it as a pusher.  A standard aeroplane prop will work fine but will need to be fitted in reverse, with the convex side towards the engine.  If this is the case you will need a Left Hand starter spring.  If you use a Left hand "pusher" prop then a standard RH starter will work.  Hope I've made it a little clearer than mud.
  

Rod.

That's some GREAT advice from "Rod".. I'd recommend copy/pasting his post into a "word-doc." or similar. A 5" x 3" 3-blade "pusher" prop would be a good choice for an airboat.. or the same size "tractor"; mounted as Rod suggested. It depends on if your engine faces forward or backward. "Backward" would be my choice.. because of ease of starting and operation.. and also if you use an external fuel tank and servo for a throttle. Those items should be amid-ship; forward of the engine. Be sure to make a "shroud" for around the prop. Cutting a piece out of a small plastic pail works well.

BTW.. I'm making mounts for the red "postage-stamp" back-plate that you have. If you can locate a needle, you could keep that engine together... A 1 ounce "Sullivan" clunk-style fuel tank would provide SEVERAL minutes of running if filled. Use good fuel like "Sig's Champion 25% nitro".. It has the correct blend of castor-oil to protect your Cox engine.

As far as a "throttle" is concerned.. "Cox International" in Canada, has a back-plate with a throttle, that would replace your red "postage-stamp" back-plate. Just make sure that you get all the parts that you need; like the reed-holder, gasket set and screws.. etc. (I'm not sure what the throttled back-plate comes with) Tiny "nano-servos", a lightweight LiFe receiver battery pack and two-channel 2.4GHz radio would complete the package!

"PM" me, if you're interested in mounts for the red back-plate.

Good luck.. and keep us informed on the progress of the model!

  Great advice from all. I will keep you guys posted.