Solved the libcurl.so.3 problem. It appears that the script used to install PHP from the Site Manager fails to update /etc/ld.so.cache. As a result, the make process finds licurl.so.3 in /usr/local/bin and builds this into the executable. However, when you try running the executable, there is no entry in /etc/ld.so.cache and so it fails.
To fix this, you need to run ldconfig -v from the prompt of your SSH session.
To check if you have this problem, use the command
ld config -p | grep libcurl
libcurl.so.3.0.0 (libc6) => /usr/local/lib/libcurl.so.3.0.0
libcurl.so.3 (libc6) => /usr/local/lib/libcurl.so.3
libcurl.so.2 (libc6) => /lib/libcurl.so.2
libcurl.so.1 (libc6) => /lib/libcurl.so.1
libcurl.so (libc6) => /lib/libcurl.so
libcurl.so (libc6) => /usr/local/lib/libcurl.so
Once I had fixed this, I tried a completely fresh install and all I needed was ./configure --prefix=/usr/mylocal during the build