it may be easy to get the same amount of power from the a series but it wont be as reliable as a standard engine producing the same power. plus you have 5 gears which is a bonus. with the allspeed frame it uses mini suspension so would still handle as well as an a series mini. vauxhall gets my vote.Ive got a 1430 with race head, 286 cam, 1.5:1 ratio rockers, 11 arp studs, long stroke nitrocarbonised cross drilled crank, all of the threads have been tapped out a size on the block to hold the gearbox on, Xpin dif, straight cut transfer gears, 2 core rad, 13 row oil cooler, leccy fuel pump... and itll be quick enough! And a very strong engine too.
Its easy to get that kinda power from an A series, but its harder to make it drivable. But over an 8v vax engine..... id choose the A series every time, really raw delivery, nice sound, original, you get to keep the A series subframe rather than sometimes switching to a K series when it stops feeling like a mini and just looks like one.
Alex votes A series
You could always look at the 2 litre 8 valve engine as well for even more power