A couple suggestions......find a competent automotive machinist who has a history with Inline GM engines and be ready pay a little extra to get name brand replacement parts. I'd avoid the "rebuild kits" that feature the majority of "Offshore" parts and build on the mindset that the 4 main bearing 261 was initially a "torque builder" engine. Trying to nurse more revs out of a torque engine is just going to cost you big bucks and leave you disappointed with the end result.
By capitalizing on the low-end torque you can set up your GEARING to maximize the potential of your engine. I see no reason to spin a low rpm/high torque engine out of it's torque band. You'll extend your engine's service life, have better fuel economy and overall improved performance. I'm currently running a .72 S10 T5 transmission but have found the Camaro W/C T5 has an even better gear spread which will maximize performance within the torque band. If you haven't driven a GM Inline 6 with a 5 speed (and the correct gearing) you've missed a really fun experience.
As was pointed out, there are numerous "standard" add-on parts to slightly improve performance....some inexpensive machine shop modifications such as drilling the crank for a SBC harmonic balancer bolt to draw on your H/B, tweaking your full-flow filtering system, modifying the timing cover so it can be pulled without dropping the pan, and I also suggest a full rotational balance. So why balance a low-rpm engine? On my 60-235 we found a 13 gram differential in rod weights in the running core I purchased. Regardless of what anybody says, I'm thoroughly convinced it was additional money well spent.
The whole key to getting a good running engine is to find a really competent, enthusiastic engine machinist/builder. There are some little improvements he can suggest that will insure you get the most bang for your buck.
Dave
