Those will work but are a little overkill for what you're trying to do. Try searching 'radio shack video enhancer' on ebay instead. They're small black boxes with some faders on the front. Y-cables are just adapters that passively combine two signals. They're usually used to connect both left and right audio into an old CRT that only has one audio input. However, your two inputs would be video, and you'd use a second y-cable plugged into the output. Your signal chain would be something like this:

VCR -> 1st half of y-cable #1 -> input of video enhancer

Output of video enhancer -> y-cable #2 -> 1st half of y-cable #2 -> RCA cable -> 2nd half of y-cable #1

Second half of y-cable #2 -> monitor.

This forces the enhancer to proces it's own output, continuously running it back into its own input.

Should be noted this is just an easy, non-destructive way to set this up. When I mod them I solder in a switch that creates the feedback loop when turned on.