Front wheel bearings interchange list of part numbers from various sources, equal to BMC part numbers for MGA. You will get the idea pretty quick here, just ask for 6304 and/or 6306, and you will get the same bearings from at least a dozen different manufacturers, including NTN, FAG, SKF, INA, NSK, NACHI, TIMKEN, IKO, KOYO, LYC, NTN.

Generic dimensions (in inches) for the front wheel bearings are:
Bearing - front hub outer, 1500/1600
ID=0.7874" (20.0-mm) -- OD=2.0472" (52.0-mm) -- W=0.5906" (15.0-mm)
Bearing - front hub inner, 1500/1600
ID=1.1811" (30.0-mm) -- OD=2.8346" (72.0-mm) -- W=0.7480" (19.0-mm)

Bearing, front hub outer, MGA 1500/1600  
ACF4000             BMC, British Leyland
9MJ20               R&M
125-400             Moss Motors USA
5-728               Victoria British
6304                AHR
6304                Brown & Gammons
6304                Dynaroll
6304                FAG
6304                Moss Motors UK
6304                NACHI
6304J *             NAPA
6304                NSK
6304 JEM *          SKF
6304                SNH (Sin Nan Hwa)
6304                Timken
 304WB ?            Timken
6304                Torrington Wuxi
	
Bearing, front hub inner, MGA 1500/1600  
ACF4002             BMC, British Leyland
23MJ30              R&M
125-500             Moss Motors USA
5-725               Victoria British
6306                Brown & Gammons
6306                Dynaroll
6306                FAG
6306                Moss Motors UK
6306                NACHI
6306J *             NAPA
6306                NSK
6306 2ZJEM UE01 **  SKF
6306                SNH (Sin Nan Hwa)
6306                Timken
 306TB ?            Timken
6306                Torrington Wuxi

* J = stamped steel ball retainer (standard issue unless otherwise specified). EM = Electric Motor application, high speed, constant load, quiet running. JEM = C3 class internal running clearance, which is about 40% larger clearance than normal C0,CN (but still small clearance).
** Z = one shield. 2Z = 2 shields. Shields are not needed and prefer to omit them for this application.

Below, original R&M bearings from MGA front wheel hub.

For MGA Twin Cam and "Deluxe" tapered roller bearings, see article TC-212.
For changing ball bearings to tapered roller bearings, see FS-206 and FS-206B.