[HWYSTR455]

Here's an example of crossmember/trans mount shims:

https://www.crossmembers.com/product...ions-set-of-4/

Some make them in different thicknesses, but it's really not that exact of a science.

If you run out of room on your floorboards, you can always jack the car up slightly by using a floor jack with a 8x8 piece of wood or other material of choice, on the floor pan above the trans mount, and jack it up some. You can open a door and jump on the door sill if it's not cooperating. Many cars over time have the floor pans sag, very common issue.

One way to check for floor pan sag is if the car has bucket seats, the headrests tip towards each other, towards the center of the car.

If it's a bench seat, or at the moment no seats, you can use a level across the seat bracket on each side of the tunnel.

EDIT: You can also in a pinch add washers to the body mounts, but that will cause a ripple effect where you have to re-align panels.

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