LS blocks

[badazz81z28]

Sorry if this seems like a stupid question or if it’s been answered before but I’m trying to figure out if/and/or which LS engine blocks are the same as in overall mount up / size?
my problem is I originally had a cracked LS7 block to mock up my engine and trans set up. The shop that had my car supposedly finished all the trimming and whatever they needed to fabricate the new firewall for my car. I picked up the empty block and trans took them home sold the block. That was about 2 years ago. Fast forward to present times I’m frustrated and want my car back since that shop hasn’t done anything with it and now I have a car with my firewall FML!! So I now need a mock up block and trans. I have the bare case trans but need a block. So my question really is can I find an old blown up LS2/LS3/LS1/LQ? To install in the mean time for the mock up cut and trim and install of the firewall panel?? I do have a short block LS7 that’s being built for the car but don’t want to install it because of the weight and ease of shifting the block around. Any help would be appreciated. Thanks.

All GM factory LS blocks are the same dimensionally.