Hey John, this topic has been covered before, but I never miss an oportunity to crap on about my motor
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These are the mods I did to my 138.
The bottom end was fully balanced, 40thou oversize pistons fitted, the head was decked 40 thou, ported, polished and port matched to manifolds. The valves are s/s red motor and the valve springs are 350 chev.
The cam is a mild one from clive cams, i can get the specs for you if you like.
I'm running twin carbs (stromberg) and extractors and a 2 1/4" exhaust.
As far as performance goes, the car has 100 rwhp, it will idle smoothly, doesn't get hot and hasn't lost too much torque so the 3 speed works well with this combo.
Hope this info helps you out
Cheers
Jason