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... Legend makes a resin Stryker engine...
That won't work either. They don't look the part, and I photographed it for Legend a few years ago - far too large.
Since you need a V-8 gas motor, I'd try a Snap-tite NASCAR model first. I grafted one into a 1/32 Malibu Police Cruiser. They're pretty easy to find. If it's too small (but I think it'll be just right) you can try any of a number of AMT/ERTL 1/25 car kits. A lot of them have V-8s.
I think you'll have better luck with the 1/32 motor. Fortunately the BRDM-2 motor's valve covers are smooth, so rounding the appropriate sized evergreen stock should give you the right look in minutes. Once you find the right return roller for the air cleaner you're in business.