mark 1's dont have a subframe...
The only thing is the captive nuts that the subframe bolts into can shear off..This means cutting holes in the floor and weldsing the nuts back down, then weld the floor back up etc... I didn't have this problem fortunately!
I don't think a semi will give the same results
Those captive nut issue is scaring me now. I just hope mine is fine when i come to take my subframe off in a week or so