I need a good arm to mate with a modified Lenco L75

If you are going to go "all the way" or even "most of the way" with your modified Lenco, then it will merit the best tonearm you can afford and fit to your plinth. Beyond that, I don't believe there are any limitations to be based solely on the fact that you have a Lenco vs some other brand or type of turntable.  It's more important to match your tonearm with your choice of cartridge.

I have a highly modified Lenco in a slate plinth.  I chose a Dynavector DV505 tonearm for that turntable, mostly because it is one of only a limited number of tonearms that can be surface mounted.  (Others include the Triplanar and the Reed tonearms.)  Surface mounting makes it unnecessary to create a removable tonearm mount that would need to be drilled out.  So my choice was largely pragmatic: the DV505 is excellent, is less expensive than those other options I named (though I do own one of each), and was convenient to mount.

I have a Artisan Fidelity modded Lenco and that table deserves that best arm I can buy.  I have a SME arm by no means the best but still a great arm.  I wouldn't hesitate putting a Reed, Schroeder or any top rated arm on a Lenco.  However it is more important matching the arm and cartridge and just having a fancy arm that doesn't match well with a particular cartridge.

In the hardcore Lenco cult (I mean that in the good sense ;-), the TransFi Terminator is developing the reputation as a great arm for the table. Unlike the Eminent Technology---also a linear-tracker of course, the TransFi is positioned on the rear of the table, running left-to-right, not front-to-back on the right side of the table.

bdp24, The position of the LT tonearm might only matter if you are using a Lenco still with its original plinth where the chassis is supported on flexible supports.  Most guys who upgrade are using massive unsprung plinths; the tonearm could be mounted anywhere without much effect.

True Lew, but I wasn't thinking in terms of the moving mass of the arm wand (one reason the VPI tables, especially the TNT's, were a great platform for the ET arm). I mentioned it 'cause I never liked having to bend over the table and look sideways to see the stylus for cueing, etc. It's nice having the arm, cartridge, and LP groove facing you! But that comes at a price---the Terminator sits over the platter, requiring care in getting LP's on and off. Being a longtime Townshend Rock owner, I'm use to that!