Hi mcmoo
The section you're referring to is taken from the LVV engine and drive-train conversion standard. There are no specific guidelines or restrictions as such, and if you read further on in this same section, it does give you a series of things to make a point of doing, or ensuring; for example strengthening the cross-members, or upgrading the stub axles, suspension etc. I've copied the section again here for you. I hope this helps!
Low Volume Vehicle Standard 85-40(00) (Engine & Drive-train Conversions)
2.2 Engine conversion requirements - Engine weight
2.2(17) A low volume vehicle fitted with an engine that is substantially heavier
than the original engine, and is of a configuration never intended by the
original vehicle manufacturer for fitment to the vehicle in question, must
have:
(a) a means of preventing the chassis or sub-frame rails from spreading
apart as a result of the additional weight or torque loading of the
new engine; and
(b) the springs and shock absorbers up-rated as necessary to support
the additional weight of the new engine; and
(c) an engine cross-member beam, if fitted, that is either:
(i) strong enough to withstand the additional weight or torque
loading of the new engine; or
(ii) be reinforced to provide the necessary additional strength;
and
(d) the road wheel hub assembly’s load capability increased by having
either:
(i) the hub assembly replaced with one which has an increased
number of studs, or pitch circle diameter; or
(ii) the original wheel studs replaced by studs of a diameter
equivalent to a production vehicle that has a similar engine
weight and number of wheel studs.
Here's a link to the LVV Standard;
www.lvvta.org.nz/documents/standards/LVVTA_STD_Engine_&_Drive-train_Conversions.pdf
