His engine is flat everywhere though, not just in the mid-range where TVIS makes a difference. With the specs it's supposed to have, he should be making 140-150hp at the wheels and a lot more midrange than he has now. I can't see how adding TVIS would help in the slightest in this instance?

The last engine I built was a standard small-port bottom end with a bit shaved off the deck, a shaved big-port head, some mild cams and a good clean up and de-dagging of the ports and chambers. Made more power and torque everywhere on the engine dyno with the TVIS butterflies and shafts removed and the holes filled than when it was working testing them back to back as I had two plates to try. Was a standard MAP big-port ECU as well so zero correction for it either way. On a standard engine it works how it's supposed to, anything more than a mild set of cams, a little extra comp and some porting and it becomes redundant.

At the end of the day all of this is moot, as I don't think your engine is as it's supposed to be. Only way to know for sure is to pull the sump off and see, or just be content to drive it as it is now because you won't be able to pull much more out of just a tune.