I'd agree with Jelly on this one. Any heavy duty 15w-40 or 15w-50 will do the job. The diesel oils typically have higher detergent levels to keep the inside of the engine fairly clean.
Also, even if this engine is still running fine - it is time for a rebuild just to freshen it up if you plan to keep this bike for a while. While the top end may only have .002 of wear, there are other parts that need attention. The stock breather gear is plastic and slowly picks up metal shavings that become part of the gear. These shavings gradually wear the surrounding parts away like sandpaper would. The hydraulic lifters are probably completely shot by this point. The stator spline should be pretty well worn away (this can be fixed without an engine rebuild) and this will eventually leave you stranded.
Plus, the best reason to get this engine rebuilt (by somebody who knows what they are doing) is that it will eliminate all oil leaks.
FYI, the first version of the EVO engine was pretty much a shovelhead with different cylinders and heads. In '92 Harley released another version of the EVO. Externally, it looked the same, but there were many improvments inside the engine - the PCV system was greatly improved. Overall, I consider this to be a better engine than the TC88.
[ March 12, 2004, 06:44 PM: Message edited by: medic ]