rindress,
Yes, an oil pump from a 3 main bearing MGA and the early Bs will work. The one main difference is the side mounted pickup of the E1 vs a top mounted pickup of the BMC stuff. Both Victoria British (VB) and Moss Motors (MM) sell the oil pump; however, you will need to source a side mounted pickup from eBay or a MGA/B forum. All gaskets from the MGA/B are the same for the E1. Otherwise no modifications are required and there are no clearance issues.
Sorry somewhere I had a side by side pic of the Nissan OE oil pump and a new BMC type pump that I took down at VB, just cannot locate it.
Found it -
https://www.flickr.com/photos/113742723 ... datetaken/
If Ted has an extra, I'd recommend this route.
Andy