🚀 go-pugleaf

There are several options for video overlay with Mac II's.  It 
basically comes down to how much money you have to spend.

The bottom end is covered by the Mass Micro Colorspace II
card, which does an overlay of Mac graphics and video based
on a key color technique and displays the result in NTSC
30 Hz interlaced video on a standard monitor.  A problem
is the flicker of horizontal line caused by the interlaced scan.
The Colorspace II can digitize still frames in a couple (< 5) of
seconds.  I believe cost is around $1200; check with a dealer.

Another product worth looking at is the Orange Micro (formerly
AST) NuView card.  This card digitizes an RGB video signal in
real-time and writes it into the Mac II graphics frame buffer.
This is not an overlay perse, but it does provide video-in-a-window
on a standard Mac color display.  The problem is that the NuBus
in the Mac will run fast enough to allow display of only about 15 
frames/s.  Cost around $1300 plus an NTSC to RGB converter.

Truevision has the NuVista card.  This is a real-time frame grabber
with its own frame buffer that is Quickdraw compatible.  It also has
a TI 34010 graphics/DSP processor on-board and requires a multisync
monitor.  Cost is > $6500, I think.

Prices are VERY uncertain, and there is no implied endorsement or
criticism of any of these products.
products.

p.s. Apple has recently started shipping an overlay card for the
Apple IIGS that sells for less than $1000.

You can never tell...