Its the best thing i have ever did to my rally car and i used to have a 63A five speed. the Toyota box it strong and the ratios are better and the hole conversion was very easy.
Ok. I also think the problem is valve bounce, the Rolla Rockers actually weigh 10g more than standard. Jeff Taylor thinks the clearance isn't the problem but he uses a relatively light double valve spring. I will try some heavier spring later. but for now just leaving it as it is.
No problems, just give Jeff Taylor a call he will sell you a NISMO one for about $150. but I would probably just get the head shaved to true it up and use a standard head gasket at about $25.
I do have lash caps and i have a JTS 247A CAM with .430 lift the rockers are the 1.54 ones. when i built the engine i checked and i had .040" clearance at full lift.