I can't help on a 3600, but I know that on my '51 3100, the second cross sill sits right behind the shock mount. But if it were put any farther back, it would be higher on the frame hump and likely hit the frame with the blocks in place for mounting.

I'd give Mar-K a call about it. Maybe send them your pictures.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.