I think that Mappy Arrangement may be easier to port then the original Mappy release (who would have thought a sequel could do that!?)
Reasons:
Less Cats, up to 5 instead of 20 cats (Not including Nyamco)
25 screens, so is viable to store every level & pre-calc scrolling in ROM
2 of those screens are identical
The trampolines also get thinner and change color when bounced on, so ditching the color for thinning trampolines would be possible
2 Levels don't thin the trampolines at all
Two Notes:
Would it be possible to have the two bosses at the original size? (about 3 of the 5 platforms tall, 1 platform wide)
There are 'worlds' with their own background, music, & platform style. Is that possible?