The size of the battery tray is 10.04 x 6.89 Inches (255 mm x 175 mm).

The batteries are 241 mm or 278 mm long, which means, the 241 mm ones will fit in, the other ones won't. The strongest battery in the 241 range was the Exide 640 with 640 CCA. You think, that might be not enough.

I would prefer a stronger one, too, but if you think I should stay within the limits of the tray…!? I could build an interim solution and make a larger tray until the engine smoothed up. But I think I could attach a bigger battery just on top of the tray with some restraints.

I will do a test run with my Corvette battery, which has something about 540 CCA. If the warm engine of the Bird can be started with that, I will go for the Exide 640. If not, I will have to think bigger!