Yes I have dropped a 2013 6.0 / 6l90 in a 1956 3100
The swap is really straight forward if you have all the harnesses and computers.
And the nice thing is you even have the body control module so even more restomod options are available.
I would buy the tuner software so you can easily program the ECM as needed. (I used HP tuners but there are plenty of guys using others EFI live et)
Mountains of information on LS swaps on the internet. Videos, forums etc Bet you can even find one on the 81 getting a LS put in.
Only note of issues that I had to chase down. MY ECM required I delete the starter check along with the VATS and normal stuff. Took a while to find that one.
Soon as I got that set it fired right up.
Mounting should be straight forward.
