Agine do not use a nutted bolt unless the bottom side of the beam is paralell to the top side of the beam. Using nuts on a slanted seat will cause the bolt to bend and fail everytime and if you go trying to grind flat seats into the beam then you are severely compromising the entire engine mount.

Using sheet metal screws is and has been a standard for years and works very well as long as you use the proper tap drill size for the screw. Much easier than tappping for a bolt as perfect alighnment is not as critical.

Also keep in mind in many installations where a hard mounted cowl ring and half cowl are used it will be imposible to access those nasty nuts.

Sheet metal screws work with the plastic mounts perfectly when properly installed (using the proper drill size for the indicated screw) easier than any other method and requiree no tap and allow easy engine removal or installation when half cowls with a cowl ring are used.

Dave Brown mounts (my favorites) because of more mounting versatility and options due to the round firewall portion and non square bolt pattern all includes the proper sheet metal screw size with each mount up to the 120 mounts which use #8 screws.

John