Heyer question

I'm rereading The Reluctant Widow and am wondering: does anyone have a good photo-reference for Bouncer? I know roughly what a Mastiff looks like, and by lurcher, I imagine Heyer most probably means a Greyhound-Collie cross, but I'm having a rather difficult time imagining how the three would go together. Aside from the part where Bouncer is clearly a Very Large Dog.

Since it seems unlikely that anyone out there actually has a Greyhound/Collie/Mastiff cross and has put pictures of same on the int