Jono:
I have the original manual for my 30 year old 67C, but don't have a pdf version. Here, however, is a good source for Beseler manuals and other accessories:
http://stores.ebay.ca/KHB-Photografix
Otherwise, I'll help as best as I can.
You will need a longer lens. Anything between 75mm through 90mm will be helpful. Do you have a regular column, or a longer "XL" column? If the column is the shorter of the two, you may prefer the 75mm lens.
What is the exact name on your existing lens? If it says something like "Beseler Color Pro" it is probably quite good. If it says "Beselar"', you might find it a good idea to replace it as well. Those basic "kit" lenses are not the best.
If you are going to have two lenses, it can be a really good idea to get two of the same type. You are more likely to get consistent contrast between the two, and it is really handy if the aperture scales and other adjustments work the same way. Not a critical concern, but surely one of convenience.
I would certainly try to get a lens board for each lens. It is so much more convenient, and they tend to go quite cheaply on Ebay (I know, because I've bought a few, and check my "Beseler (not Topcon)" eBay search almost daily).
Be careful though - Beseler made (and still makes) the 67 series lensboards with more than one size hole, and in addition, with a pilot hole, for lenses that require a custom size. You need to be sure that you get the right size hole.
Three cautions:
1) although most modern lenses in these focal lengths have 39mm threads, not all of them do;
2) as mentioned above, some of these lensboards either have unusual size holes, or have just a pilot hole, because they are designed to be drilled to fit custom sizes; and
3) you will need an appropriately sized retaining ring to keep the lens mounted to the lensboard.
Good quality used 6 element (usually) enlarger lenses are readily available, and could potentially make a real difference to you.
Hope this helps.
Matt