I read your info...
MCG made up some T shirts with the "243 mph" on it, implying it was done at the Chelsea Proving Grounds.
A little high from the actual top speed of 205 that Glotzbach ran!
I talked to the guys that were there. 205. Not any higher with a 575 hp nascar engine.
Now, it would go faster with Nitrous on a dual carb race hemi.....
So, depending on how much HP you have, that will determine top end.
I'd say at any speed, the car would be stable enough. Have to have tires that would work, too.