Just to clarify.
My answer and Galahad's are absolutely not in opposition.
His approach would be to 'exceed' the limits by rewriting the code to use a software system for object blitting
(rendering in fastram with a fast processor and using the chipram as a frame buffer or something in between).
In that case the engine could maintain a decent framerate.
My proposal, on the other hand, would not improve the frame-rate in any way, but it would simply delay the refresh (making duplicate frames).
In any case it'll remains a game designed for A500 and you can not expect more than that in this conversion.
Any kind of drastical change will require too time that maybe the coders/patchers prefer to use for other
