You’ll get what you pay for, but none of them will be as good as an original. Show us a pic if you don’t know if you have a T2 or T25 type 4 alternator.
I would try it with a new battery or at least a known good old one before fiddling with alternators. 17 volts is a massively trashed battery or alternator with wiring problem not necessarily either the alternator or regulator.. like field shorted to battery.
Here's our spare, just back from being reconditioned . Type 4 GE code for reference. Output 14v 70 amps
It's a solid state one like this that's fitted to the van currently. The bloke that did the recon sent this one out as a spare! Works really well and is a simple, low cost upgrade.
No fan on the 55 amp. But you do need the back cover and cooling air boot and the adjuster slot cover on the front.