What do you mean with "underfelt"?
Never seen anything other than a bitumen mastic kind of anti resonance material on a TR7.
On the DHC I removed everything and replaced it with this product from 3M ...
Lighter and better sound proofing compared to the original material.
<center>
<font color="blue"><i>1976 TR7 FHC (currently being restored ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
</font id="blue"><b>[url="http://www.tr7beans.blogspot.com/"]<u><b><font size="2"><font color="red">Click this link for a full version of this blog</font id="red"></font id="size2"></b></u>[/url]</b></i></center>