On December 3rd of 2000, Greg came to my city of Thunder Bay, Canada [which is in the province of Ontario, where Greg was born and raised, and I lived in until his death], and my friend told me that Greg had allegedly suffered, as you quoted, 2-3 heart attacks.
I have no idea if that was true. When he came to Thunder Bay, he was tipping the scales just north of 400-lb. He may have been around 410, something like that.
On Canada's "MUSCLE INSIDER" magazine's website, Greg stated that he was 365-lb in 2012, just under two years before he died. On a radio/podcast interview with Dave Palumbo, Greg also stated that if he had it is way, he would just train for fun, and weigh around 400-lb.
So clearly, he enjoyed being 400-lb at 25% body fat, or whatever percentage he was at, despite the pain that came with it.
Given that Greg died in 2013 and was 365-lb in 2012, I think that it is safe to say that he was likely around 365-lb when he passed away. Here is the MUSCLE INSIDER article where he stated that his max weight was 412-lb:
https://muscleinsider.com/columns/average-bodybuilding-diet
In this MUSCLE INSIDER article/interview, Greg states that his max weight was 416-lb:
https://muscleinsider.com/features/lost-interview-one-one-greg-kovacs
In other articles - also on MUSCLE INSIDER - Greg stated that he weighed between 410-420, and that fans would be disappointed if he showed up to an appearance weighing 395-lb, rather than 400-lb. That must have played on his Bigorexia a lot. 
Tony Doherty - long time promoter of the Australia Pro Show - stated that Greg was quite insecure. The stories were sad.
I think we can most likely state with confidence that Greg weighed over 400-lb between 1995-2005, and that even going back as far as Greg's 19th birthday in December of 1987, he was almost surely around 290-lb and ripped.
Greg was likely over 300-lb from 1986-2013 [aside from early contests that Greg competed in between 1989-1994, where he cut down to as light as 270-lb, literally at the very lightest, and that would have only been in 1989-1990].
Think about that:
Greg spent 27 of his [just under] 45 years of life weighing over 300-lb.
Greg spent around 10 of those 27 years weighing over 400-lb.
The latter fact is probably the most significant one to think about when considering the toll on his cardiovascular system - between 1995-2005, aside from the four contests he competed in [turning pro in 1996, then the 1997 NOC, and both the 1998/2001 Ironman contests, the last of which he dropped out of], Greg was consistently 400-lb or more at 6'2.
For some appearances, he may have weighed a little less, but even at those times, he would have been taxing his body by using cutting agents to lose weight.
All this considered, Greg led a unique, but in my opinion, ultimately sad life.
Here is a video I did showing some rare photos of Greg, posted by his sister on her Facebook page, tagged with Greg's name:
is it because you have a short person complex you have to downregulate other peoples heights?
He was 6'4, fyi.
