At the time of Sijo Lee's death, he was WALKING at about 135-140 lbs. 147 tops. Earlier, he was about 150, prior to intensifying his workouts. As Nelson stated, Sijo was a workaholic and was working insane hours prior to his death. He was involved in every aspect of his Hong Kong films, from editing, scripting, directing, and fight choreagraphy. Not to mention his own training.
As far as these debates over his competion (or lack thereof) or where he would be in modern MMA; we have to understand his premise and point to training-REAL fighting in self-defense. Period. He would probably love MMA and see the merits, but he was not concerned with points or winning rounds, but self-defense aspects.
Now onto some specifics:
Sijo practiced amateur Boxing in his youth and did enter at least one tournament, winning in his weight category I believe.
He also practiced and competed in fencing, which is where he got a lot of inspiration for his footwork and "strong hand forward" thinking.
He studied Wing Chun Gung Fu from when he was quite young. He also ran with street gangs in Hong Kong (which are no joke) and was in MANY street fights, often fighting with a chain from an old style toilet he kept hidden by wrapping around his waist. He would use it as a whip, or distance weapon. The gangs often fought each other, and had one on one challenge matches on the rooftops of Hong Kong.
Bruce Lee studied many diverse styles. He was doing an extensive amount of wrestling, Judo, and Ju Jutsu at the time of his death. He had a great deal of respect for grappling in general. He was often quoted as saying that a high school or college wrestler with a little boxing would beat any martial artist of his time.
From first person accounts that I have been involved in, (reputable Bruce Lee student accounts) Sijo Lee had incredible hand-eye coordination, hand and footspeed, balance, and tremendous power. The closest people that I have seen today, possesing many or all of his attributes are Manny Pacquiao and Kru Phil Nurse. Both of them are about the same size, and possess the same power, speed, and balance. Phil is unbelievable to watch and train with. He's the closest "martial art" person living that has the same attributes.
We can consider Sijo Bruce Lee as the Father of modern MMA in the sense that he showed the reality, as the Gracie's did with their Gracie Challenge and starting the UFC, that if you have the Hubris to think studying only one discipline is enough, then you are sadly mistaken. As we've seen in each evolutionary step of MMA: if you are only good in one range, you'll only go so far. You MUST have a solid understanding of ALL ranges of combat: weapons, striking, grappling, in order to be truly a martial artist. All ancient martial arts knew this, and worked on various ranges. In Modern Times we've forgotten this.
So... YES-Bruce Lee is the "Godfather" of MMA, but he was so much more than that.