is there any pre-fab engine mounts to install a L33 into a stock 1957 chevy stepside truck frame?
Thanks

 

1957 what??

 

a 1957 chey stepside truck

 

I don't know of anyone making LS mounts for those trucks.
Shouldn't be too hard to cobble something from a crossmember kit from Trans Dapt or similar.

 

Holley has a extensive line of LS swap parts...check them out

 

Pic of the frame with the LS more or less in position with the "typical" LS side mount plates bolted to the engine? That would give us an idea what might work. Long before Holley had the Wrangler swap kit I used a frame side mount kit for a street rod frame. Basically an L bracket with a rubber biscuit for an isolator. Got them from Speedway. Then I had a couple of 45 degree 1/4" plates bent to attach the engine plates to the frame mounts.
Not a great pic but you can just see them on my 98 Wrangler on the passenger side. They are gold colored with a small gusset.

 

2 minutes on google found this. It should be a pretty easy job to fab something if you don't find something you like.

https://www.performanceonline.com/19...ossmember-kit/