how much of a canbus network is REQUIRED?

[ottawa coupe]

so, i am back on the engine swap train given some life circumstances. there are 3 swaps in contention.

the first is an AAN which is period correct i suppose, but packaging will be challenging considering the parts i have left on hand.

the other 2 are more modern engine swaps with canbus architecture.

one is a complete b5 s4 that has rotted away thanks to canadian road salt. cheap, complete, and from a certain perspective easy to install from where i stand at the moment. just a lot of plumbing to sort. $ wise, by far the best as i can sell a lot of stuff i don't need for good money.

the last possibility is a c5 s6 4.2 BBD motor (engine only, not complete car) with ME7.1.1.

for the v6 and 8, i believe the questions are the same. Will the tach signal be in the canbus info or is that a wire coming out of the ecu that the b3 tach will understand (i have the 7A tach as well as an AAH tach)

for diagnostics code reading, will i need the gateway? reading mk5 golf diagrams (because i have them and should be similar from a network perspective?) seems to me that the powertrain canbus network is connected directly to the obd port so i should be ok? i'd still have the kline for the old abs any whatever else spoke to obd back in those days. i would have to snip off a diag plug from somewhere as well i suppose.

i know i will need the ecu to be reprogrammed for manual transmission as well as immo defeat (and maybe i'll make my life easier with secondary o2 delete)

i am trying to make up my mind in the next week....

thanks for any help

[ottawa coupe]

I figured out diagnostic info, the laat question is tach signal. The rpm is sent from ecu to tach via canbus. Happily, tbere are aftermarket modules that will take canbus and generate a square pulse for the tach.

The last question is how many pulses per revolution on a b3 so i can get the right signal generator.