Can anyone tell me the type of flat tops used in A15s to get the biggest bore size possible.The pistons also have to be eyebrowed so need to be meaty on top.Any help would be great.

Mazda pistons are often used. I think that the ones from the MX5 sportscar thing are good. You will need to do some machining, but they can be made to work.

I use Mazda pistons
STD bore 77mm. But I guess you can go 40th oversize to get 78 easily.
They are dished.....but when installed on the A14 rod with A15 crank they would stick out the bore so the tops are machined down till you get this


Yes they are flat.
Pin hole on rod needed to be enlarged to 20mm for the Mazda gudgeon too.

Piston I used was out of a Mazda UC OHC series engine circa 1979-1981. 323 RWD and E series van.
ACL part # RY2699.
They run thin (1.5mm comp rings)

Hope this helps.

I'd like some forgies to suit...and will need some flycuts for valve clearance before the bigger cam goes in.

how much did the pistons and rings cost u as im considering the same project for my ute

I used 1mm oversize Mazda E3 pistons. Flat top. Pin height almost bang on, took a little of the block, .010" or something, and .020 off head can't remember now too long ago. Had to bore little end to 20mm same as dattoman1000. had to cut notches in top for valve clearance, had JUUUUUST enough meat, a bigger cam would have been a problem though. ACL, pretty cheap. Chrome plated top rings, 1.5mm.
Should have gone to 2mm oversize, 3mm over in the datsun to make 79mm and about 1608cc I think... Mine is 78mm and 1567cc or something like that.