Online Auto Parts and Auto Accessories Store at PartsAmerica.com list P/N 13050 alternator for 1975 Manta.
$68.99 + $20 core. It is a 50 Amp alternator; direct fit.
Google "discount coupons partsamerica" to locate 15% discount.
Opel GT Source has high amp alternators; direct fit.
Call them for latest information and prices.
5022 ALTERNATOR
Rebuilt. Specify 35 amps, 45 amps, or 55 amps. Core required. 129.00
5022-65 ALTERNATOR, HI OUTPUT
Rebuilt using Bosch 65 amps internal components. Core required. 150.00
5022-IR ALTERNATOR INTERNALLY REGULATED
Rebuilt Late 80's Opel high output regulated alternator, 45 amps. 149.00