BAE fatheads

Hi Guys im just looking for a quick bit of info so im asking the experts
Iv got a mate who has a 521 bae with bae 5's and mag intake,

hes looking at buying some good used 8's he's worried whether his intake and hedders will fit, i didn't think the 8 was much different to the 6 apart from valves and some intake port differences, and I recall years ago having 5s and replacing them with 6s without changing things,

any one got more info and a way better memory than me out there
thanks Guys