More on the pushrods.
I've put together two of the arf 60s. If you glue the pushrod tube that comes with a pushrod set inside of the already installed pushrod tube, you will end up with a little less slack in the system, and it will still be smooth. Throw away the nylon pushrods so you're not tempted to use them.

I've flown the 4*60 with a 61 two stroke, OS70 four stroke, both Saito and OS 91 four strokes, and a YS 91AC.

The 61 was too noisy and slimy, but it flew well.
The 70 FS makes a nice flier, but you don't get much vertical.
Both the OS and Saito 91 engines seem about perfect.
The YS 91AC was excessive for the plane. With enough prop to keep the engine happy, you really had to have the idle down to get it to land.

An aftermarket tailwheel is a good idea. The stock one tends to break from fatigue.

Larry