I lucked into a 12x20 contact printing frame as part of an ebay purchase. It has a 3-part split back with springs to provide pressure. It can be a little bit of a challenge to align two 8x10 or even worse 3 5x7 negatives on the paper. If it works though, the fussing around is worth the effort. Check on the Bostick & Sullivan site and see what size frames they offer. For doing 2x 8x10 in horizontal, I'd recommend a 12x20 frame, or even going up to a 20x24 frame, but still trim your paper down to 12x20 to avoid waste and have enough space to process it.

I put the split back on my work table, springs down, then put my paper on top. I align the negatives, then lower my glass on top. Static and air displacement still often cause the negatives to move around, so I often have to do this repeatedly until I get a good sandwich. Sometimes I align the negs on the glass and let the surface tension hold them in place, then lower the glass onto the paper. After the glass/neg/paper/back sandwich is made and aligned, I put the wood frame on top, flip the assembly over, and lock down the springs. Then I expose away, and process as normal.