As an active member of both the PNG and Clio Sport, and with a fair bit of Nova experience, perhaps the following may be of use.
Even when new, Novas werent known for their handling balance, and had a fairly hard ride - Vauxhalls idea of a sporting hatch. But they are honest, cheap tuneable fun (especially nowadays).
If you are considering dropping a big lump in, a chassis strengthening kit is a must - 2 litres will pull the front end apart (Ive seen it!) after a few months of interesting driving, and a turbo lump will only magnify the problem.
Yes they do have difficulty in going round corners, but thats because theres an extra 49kg hanging out front when converted to 2 litre power. They can be tamed with a few choice suspension mods. however, although I wouldnt go as far to say as they would be converted to 16v/Williams/172 etc.. levels.
Good fun in a straight line though - Friend has a standard looking GSI with 16" alloys, lowered suspension, LSD and bog standard 204bhp Calibra Turbo engine with 5 speed box (6 speed going in shortly) - runs 13.8 sec quarters all day long @ 105mph, and is his everyday car.
Although Ive recently bought a new 172 (which is fantastic), I wouldnt dream of selling my Nova as its had too much money thrown at it and you never get it back. Still gives me a huge buzz every time I drive it which isnt very often now unfortunately.
Hope this helps.
Ian H.
P.S - Quickest 1/4 mile I know of was 13.1 sec back in 1998ish. Gives you something to aim for!