The best carriers for wall projection will sandwich closed with some sort of keeper. The carriers in which the top glass just lays on the other piece are not so good. What makes you think your existing glass carriers won't work? Is there nothing to keep it closed tight when you insert them into the enlarger?
In terms of lens to negative distance. Usually one does not need to calculate that because the enlarger manual will specify which lensboard is needed and then you just focus with the bellows. If you need to eyeball the distance to figure out how much lensboard recess you need, realize that at "Mural" sizes, the lens to negative distance will be close to the lens focal length. And at 1:1 the lens will be at 2x the focal length. If you need something closer than that, use the 'thin lens formula.' (1/p +1/q = 1/f where p = neg to lens and q = lens to wall)
You figured out a way to focus, right? Maybe have your target moveable on rails for fine focus. That way you can use your grain focuser. Otherwise you will need very long arms or an assistant.
Here is a chart, but it is for 8x10 negatives: http://www.durst-pro-usa.com/pdf/Pro...0enlargers.pdf
How big will you be printing? There is a reason there are not many (any?) horizontal 4x5 enlargers and I believe it is because of the light source. If you are printing very big, you need a lot of light. Probably need your condenser head and a brighter-than-recommended bulb with a fan. For example, Bob Carnie's 4x5 setup for big enlargements uses the common Omega D condenser head but he puts a 250W bulb in there (that head is rated for 75w or 150w).
Last edited by ic-racer; 12-06-2012 at 11:18 PM. Click to view previous post history.