Finally talked my gf into having a threesome with another guy

Finally talked my gf into having a threesome with another guy. She said she’d only do it if it was a nice big one, 8" or over. We talked about it the other night while getting ready to have sex and she got so turned on by it an really started getting into it!!! One of her ex bf’s used to be black so I was thinking about trying to get ahold of him and see if he was down to do it. What do you think??