http://www.jlmaudio.com/JLM%201272%20Switch%20Kit.htm
http://www.jlmaudio.com/JLM%20Module%20&%20BA283.pdf
http://www.jlmaudio.com/JLM1272simplemod.pdf
http://www.jlmaudio.com/JLM1272hotrodmod.pdf
http://www.vintagedesign.se/diy/1290diy.htm
http://www.vintagedesign.se/transformer_cross_table.htm
http://www.technicalaudio.com/pdf/neve/1290-EN10041.pdf
http://www.technicalaudio.com/pdf/neve/1073-EH10023.pdf
http://www.technicalaudio.com/pdf/neve/0283-allvers.pdf
http://www.technicalaudio.com/pdf/neve/0284-EX10284+doc.pdf
http://www.technicalaudio.com/pdf/neve/EK20033-sensSW.pdf
http://www.danalexanderaudio.com/neve.html
http://www.seventhcirclestudios.com/SCA/SCA.htm
That should get you started.
Do be aware that the 'real' Neve class-A preamp design (as in the 1066, 1073, 1084, 1290, etc...) uses three gain stages for higher gains. The 1272, and similar designs (SCA's N72 kit) use only two stages. Higher gains can be achieved with two stages only, but the character of the sound is not be the same as the 3-stage design. This doesn't mean the 2-stage versions don't merit their existence.... they can actually sound very cool.
I'm actually about to help a friend outfit his live recording venue with 24 to as many as 40 channels of Neve-type preamps (DIY, of course!), and we're going to use both 2 and 3-stage designs, because he likes them both, and appreciates the difference.
:grin:
Much peace,
JC