i was gonna say, the AM6 is a better bet. CR80 doesnt fit like at all, so both are pretty equivalent effort building mounts. Dos might have some MB/MT80 stuff if you ask em, they used to have some but doubt theres any still.
But if youre goin CR80 you're lookin at effort pretty equivalent to any other engine swap, why not go by whatever's available. probably find a YZ motor and fit a lighting coil or somethin. like in that thread they made the whole cradle and everything.
Bobby swoops put an am6 in a ysr and that was insane fast, like 80s? and another atl fella did a YZ swap in his, also batshit fast.
The lifan motors are a pretty lame option but the nicer 190's should do 70.
Also, I got a cheap kit, HPI and homo pipe, VM20 and intake from NS and it's solidly 60. not much over but it's very ridable and keeps up unless youre tryna go on the highway. I feel like thats a pretty realisitic expectation of an MB5