My mate, "The Boss" at my local service station runs a 1200 coupe in the 1600cc class in the Supersprint series. He runs a fuel injected A15 that is bored to 79mm [the racers standard] & it displaces a whisker over 1600cc but is within permitted limits.

During last year [I think] he took the lap record for his class at Wakefield Park twice in two consecutive runs & the tachometer tell-tale didn't record 8,500 rpm [close but not that high]

If you have plenty of money & spare engines, then you can try to make a street engine haul the heaviest of the small Datsun range, the B310 Wagon at racer speeds, but better yet, start with an A15 engine as this was original fitment in the last of the Sunny wagons anyway, make it run as good as you can within a realistic budget & enjoy.

9,000rpm in a streetable A series? Not really an economic proposition unless you can comfortably part with upward of $10,000 for each engine that you have professionally built. [You would probably need a few as the life expectancy would not be all that great]

If your mates POS Commodore is quicker & faster, ... then in the end, who gives a sh1t. It won't change the course of world events if you are faster or not, but I bet you reap the benefit of your smaller car at the service station & at todays prices, I suspect he quietly envies all the extra cash that you have at the end of the week.

If you want faster with a small Datsun engine, then start with a lighter car, much lighter, like a 1200 or even a 1000 two door sedan, the lightest small Datsun passenger model that they made. Trying to haul a barge with a small engine is not the competitive edge that you seek.