a marlin roadster, for example, built and constructed in the 80ies, would never pass the IVA test without major, time andmoney consuming modifications..whereas a sportster, which was designed later, will pass easier.
even both cars look similar they are totally different.
also IVA and SVA are differnt...a car which somehow passed SVA does not fullfil the IVA standards...IVA is much stricter and more comprehensive.
to name some of the IVA requirements:
it starts with glass needs to be e-marked, light lenses need to be e-marked, windscreen wipers need a min.requested wiping-area and a requested speed, typical old chrome "smiths" instruments do not meet the IVA requirements in terms of bezel radius, iva requires certain dashboard switches and warning lamps, mirrors need a certain size and shape, indicator position, noise, all sharp corners and protuding bolts/nuts need to be covered or rounded(internal and external), door lock mechanism and door handles need to fullfill certain modern standards, you need a tethered fuel cap (Or one that uses the same key as the ignition), fuel tank cannot be near hot surfaces (e.g. exhaust), Seats must have head restraints...plus lots of things more!!
One point is particularly important. When you submit your finished car for the necessary IVA test (which will cost you at least £450, by the way, some re-test fees on top...and the majoritiy of the new designed kits even need a re-test)) it will be up to you to prove that it has been built by amateurs. Good ways of doing this are by submitting photographs of the kit being built in a domestic environment, and you will need such pictures from the seller. Also useful are receipts for parts, of which there should be a good many. If these are not available, and the kit is anything other than barely started, you probably be refused a test, or may have to dismantle the car and then rebuild it, this time with photos to prove that you have done so.
So, if photos and receipts are not available from the seller, be very wary, and better still avoid it altogether.
As regards actually getting the car on the road itself, the cost of the IVA, re-test, registration (+ a trailer?), road tax, insurance, number plates and fuel - allow at least £1000, plus all the parts you need to buy for completing the car.
here you can download the IVA manual.
this said...nothing is impossible...but you need to to make up you mind if this is worth all the hazzle....andyou already see from te above prices that you need to get the kit nearly free of charge that it finally makes sense to invest further money.
use google and type in "kit car+IVA" or " kit car project+IVA" or "pitfalls+IVA"