After some years of ownership of alfas and endless research i haven't stumped upon a list of recommended upgrades for the 156.
The list is probably 10 years late, better late than never right ?
Anyways here it goes:
(an [X] means its fitted on my 2.5 98 156)
[X] Headunit: Parrot Asteroid Classic - remember to download the official Alfa Romeo firmware
[X] Subwoofer: Pioneer TS-WX710A - Really sleek OEM look if fitted in the boot
[X] Discs: MTEC Grooved and drilled
[X] Pads: Ferodo DS2500
[X] Lines: HEL Braided Lines - alternative is Goodridge Phantoms
Airbox: BMC CDA - Remember to purchase a new Bosch MAF when upgrading to this.
Intake: Polished stainless steel intake manifold - hand made in Italy, looking really sweet with original chrome inlet runners.
[X] Battery relocated to boot - this is essential if fitting BMC CDA
[X] Gear: CLOS Quickshift (not recommended) - Go with the MTECH one or Highpower-Racing QS KIT (top stuff)
[X] Engine Mount: Original fitted with Powerflex works like a treat.
Radiator: Hand welded high flow aluminium radiator with twin water core - tested in 2.0 TS fitted nicely.
Exhaust: Wizards backbox is topstuff - heard it on a GT, its 1st on my wishlist .
Differential: Quaife Helical LSD - Autolusso seems to be the cheapest supplier.
[X] Clutch: Sachs Clutch Kit - Custom Made + Reinforced 15%
[X] Tray: Alfisti Aluminium undertray - The Jap flatout guys also makes an aluminium undertray kit its pricy though!
[X] Crystal projector head Lamp with dual CCFL rings in black housing
[X] Crystal clear repeaters
[X] Smoked tail lights
[X] GTA Multispoke 17" Dark metallic
Sideskirt: Bertucci MAR110
Spoiler: Zender bootlip - alternative Lester bootlip spoiler
[X] Damper: Koni Sport Kit (yellow) alternative is Koni FSD and since the price these days have fallen on FSD this might be the better option.
[X] Springs: Eibach Pro 30 mm.
[X] ARB: Alfastumper ARB kit front 26mm & rear 19mm - Since alfastumper is unresponsive i would recommend the Eibach Anti Roll Kit.
[X] Droplinks: Aluminati front+rear adjustable drop links - The ends are changeable and cost 12£.
[X] Wishbone (upper): FRAP with reinforced bushes are an better setup than original wishbone fitted with powerflex.
Please come with additions