So in the video, the Tsukuba monster class guys say they’re getting 120 - 130hp.
How difficult is that with a 1075? How about with an 1170?
Can most any competent engine builder accomplish this?
Porting, cams, bigger cams, exhaust, welded crankshaft, some kind of kit that makes it shim under bucket. Bigger carbs. Anything else?
First of all your quoting HP numbers from track engines on race gas, not street tuned engines on pump gas. You should post a link to the video as there are many classes and some are unlimited displacement which makes a big difference.
Even if the class limit was 1200cc you can't compare that to a street tuned engine as you can run a lot higher compression on race gas.
Pump gas limits compression ratio to about 11:1 (air cooled 2 V) most race engines are 13-14:1
HP will be variable due to port size, valve size, carb size, cam lift, and compression. HP can vary on the same displacement engines by as much as 30% (rough est) due to the components and state of tune between them. Every engine is going to be different depending on how much $$$$ you throw at it.
In all cases of hopped up engines you would want a welded crank. With cams over .410" you would want shim under tappets, there are no "kits" to make it that way, you just set the valves up to be able to use that type of bucket.