I'll give my opinion,
I would save up for the stock sized forged pistons,and put it together with what you have.You can get by with not having a lot of machine work,is it ideal? No,but it will work.The reason I think you need the forged pistons is,depending on the gear ratio/tire size,and the weight of the car,it might accelerate faster than you think.
If the r.p.m's are there,the cast pistons won't last long,and then you will have to start all over.
Good luck