JZ engines are plenty bigger and heavier, plus pricier. Fitment is even more an issue than it is with a 1G...we never got the 1G btw. And yeah BPs ARE that easy, its just more trendy to get an SR20 into a 240 than it is to get power out of a "gay car" like a Miata. I guarentee you that its cheaper and more reliable to use the Mazda engine than the SR. Period.

Also, dont forget 300 HP in a 2200 lbs chassis with a full tank and sometimes driver is a hell of a lot...its VERY different from a sturdy car like a Supra

As far as it having a chain, that doesnt mean it can come from the factory with a bad link and you wont know about it for a while. A few monthes ago I swapped 2 engines into a 745Li because the first one's timing chain broke, and it was a brand new engine from BMW. Engine had 150 miles before it broke