MGA Propshaft Tech covers that otherwise gaping space between the gearbox and the rear axle. This is one small assembly, but there are some design variations, and there can be some very serious problems.

When the splined shaft is assembled to the drive shaft it is essential that the forked yokes on both shafts have their axes parallel to each other. In other words, yoke (A) must be in alignment with yoke (B), and the flange yoke (C) must be in alignment with the flange yoke (D).

PS-101 - 3 PROPSHAFTS used in the MGA

PS-102 - The BAD U-JOINT - when to be SCARED
PS-102A - The BAD U-JOINT - What It Looks Like Inside

PS-103 - U-JOINT Cross Reference List (for MGs)

PS-150 - os - Propshafts and U-Joint Rotational Alignment.
PS-151 - U-Joint Alignment Procedure For Passenger Cars - (383-KBpdf)

PS-201 - os - U-Joint Replacement Video by University Motors, LTD - (YouTube)

PS-202 - Universal Joint REPLACEMENT SEQUENCE.
PS-203 - Universal Joint QUALITY PROBLEMS.