Deccas are strange cartridges, Patrick, and you never know where they will work next. They do like unipivots, and so on this score it should work with your Graham. They are said to prefer higher mass tonearms, but on my Black Widow, it tracks no problem, which is very strange, as the Black Widow is an ultra-low-mass tonearm with knife-edge bearings, the last thing I would think it could track in! Tbg reports good results in the Schoeder tonearm. So, my guess is that if you get a new Decca - like the one reviewed in this month's Hi Fi World - the new stylus profile (at least I have heard it is new) will make it more tonearm-friendly.
The difficulty of mounting the Lenco into a new plinth depends on how familiar you are with tools. Having the outer dimensions cut for you helps a lot in the final finish: amateur cuts with simple tools inside the 'table will not be visible. The plinth itself will be easy to drill, the Lenco top-plate is not very thick, so can be cut quite easily with a rotary tool or with a hacksaw. But you should get the tonearm aligment template and see if it won't just pop into the Lenco's own armhole. The Rega arm pops right in, but not with perfect geometry. I have just cut off the cormer of my latest Lenco L78 to allow for perfect geometry and VTA. I will post photos of this new plinth/'table soon on the Home Depot thread to give everyone an idea of how to do it.
The difficulty of mounting the Lenco into a new plinth depends on how familiar you are with tools. Having the outer dimensions cut for you helps a lot in the final finish: amateur cuts with simple tools inside the 'table will not be visible. The plinth itself will be easy to drill, the Lenco top-plate is not very thick, so can be cut quite easily with a rotary tool or with a hacksaw. But you should get the tonearm aligment template and see if it won't just pop into the Lenco's own armhole. The Rega arm pops right in, but not with perfect geometry. I have just cut off the cormer of my latest Lenco L78 to allow for perfect geometry and VTA. I will post photos of this new plinth/'table soon on the Home Depot thread to give everyone an idea of how to do it.