I didn't install the 26 in that car, it came that way; but yeah, had holes and nuts/bolts.
Found it interesting that the stock opening was present; it had top & bottom tanks, unlike the Griffin in my drag car which has side tanks.
The Griffin is a "universal Chevy" model.
Only thing - come to think of it - that I thought odd about the Griffin is the bottom hose connection is higher than the bottom of the tank.
Hasn't been a problem, though.