Just a quick question: Which diff is better:A 1200 wagon or a C20 van, which has the better ratio and how strong are they?

The C20 van -- if it has the H165 is the better differential, it's strong enough for a turbo engine and there are a range of ratios.

See the Tech Section article What Diff?.

Oh, the wagon diff is more or less the same as the coupe diff. It's better because it bolts right in, uses the stock wheel sizes and offsets.

What about the H-190 diff? Will it hold up to a worked A15 motor?Would the H-150 diff be suitable?

from what ive learnt the c20 diff is a couple of inches wider than the 1200, you would have to run front wheel drive wheels to keep the wheels inside the guards.
your best bet would be a roadstar ute diff
it uses the same centre as the c20 but is narrower and bolts strait up,shit ive just rememberd im selling one ,look me up on the classefieds.
hope this helps.

very smooth

they are apparetly a good diff, and if i remeber correctly its a good price considering the rarity of these things