I forgot to bring the camera 'cause I wanted to snap a pic or two for you Bill... I did check the bolt size into the block and I'll stand corrected, I thought they were 3/8" but they are actually 7/16" , I didn't measure for the length but I see you've already done that.

Your engine sits alot higher in the chassis than mine but the principal is the same, the general thought needs to be triangulation if your going to come off the side of the frame. When I see your setup I sort of automatically gravitate to the crossmember setup that you can find in Speedways catalog.
Ford Weld-In Motor Mounts - Speedway Motors, America's Oldest Speed Shop also look to the bottom of that page as that is the complete crossmember with mounts that I was thinking of. If nothing else there are a couple ideas there...

Hope this helps...