I've a little experience with those bushings in that application, they tend to be harsh. OK for a race vehicle, not great for anything street driven if the engine isn't really smooth running to start with. I suspect that they're not going to be soft enough or have enough deflection is this application. I used rubber bushings (FJ60 leaf spring eyelet bushings) in a similar mount lay-out for an abandoned project. I wish that I'd gotten to the point of being able to start that SBC because I was concerned that rubber wasn't going to be enough and I'd like to have known one way or the other.