2F/2F -

I have a totally different set than you because I turned my Kodak 8 x 10 2D into a horizontal enlarger. The normal lens I use for 16 x 20 enlargements is a Rodenstock Rodagon 300mm. But for blowing up only part of the neg, I use a 240 El Nikkor F5.6 lens and it works great. I'm pretty sure that it would also work with the full negative.