RC;
"...dynamo on the left of the engine near the exhaust manifold. This would be an undesirable location for an alternator so I presume this was the reason to switch to the right of the engine..."
...this location is no less desirable than the Dynamo/Generator location of the earlier cars...in fact, even the early RHD cars also had their Dynamo located on the Manifold side, so there must have been room (maybe it was just "tight")... but this begs the question: How was there room for the Dynamo, but not the Alt on RHD cars (which I cannot answer...maybe OD of a Dyn is less than OD of an Alt...someone with a RHD Amazon can chime in with some pix). I thought a major reason that the Alt was moved to the Distrib side was to clear the Steering Box on RHD chassis, but this was clearly not absolutely necessary...I accept the minor advantage of cooling.
If you are going to use the B18 and must locate the Alt on the Distrib side, you will need a custom support bracket fabricated (I expect this might be involved and expensive)...but given the above with respect to there being adequate room on the Manifold side, an alternate solution would be to fit one of the retrofitted Alt brackets available (which add the Alt pivot to a similar location as shown below), onto the three OE Dynamo bracket holes. This might be a simpler, less costly solution than having the custom bracketry designed and fabricated for the Distrib side. ...hope that helps...
Source:
https://www.sw-em.com/altkit_additio...n_B18_and_B20s
Good Hunting!