Inside of sills need strengthening.
But you also need to brace the inside of the B-pillar ...
And a welded in stiffning brace/plate in the boot ...
Also rear deck and top of window frame needs altering etc.
To keep it short, I wouldn't recommend it
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<font color="blue"><i>1981 TR7 FHC Sprint (better known as 't Kreng)
1981 TR7 DHC (not very well known yet, but back on the road)
Also a 1980 TR7 DHC, 1980 TR7 DHC FI, 1981 TR7 FHC
http://tr7beans.blogspot.com/</i></font id="blue"></center>