The early Minor did not have the plate front spring (Pt No: ACA5271 (MOSS)). The large head of the pin (Pt No: ACA5305 (MOSS)) was just fitted into the spring hanger.
The revised spring hanger and front spring plate were fitted in response to the spring hanger wearing and allowing the large head of the pin to rattle in the spring hanger. The spring front plate became a sacrificial plate (easily renewable instead of renewing the whole spring hanger).
I have posted above a photo of the both the inner and outer plate and it can be seen that there is no large hole - the inner plate just bolts on top of the plate front spring. The pin (Pt No: ACH5180 (MOSS) from chassis No: 497583) is fitted before the inner plate is bolted on.
Whilst the access to the two 1/4" (or 5/16") plate front spring bolt heads is tight they are accessible.
If you want a straight bolt on anti tramp bar system here is the link to the ESM kit :-http://www.morrisminorspares.com/rear-s ... up-p831360
Note that the side plates do not have a large hole in them to allow fitment or removal if the pin.