If it were me, I would measure the twist first by laying the frame on its side and then shimming the frame until a spirit level on the HT read level. Transfer the spirit level to the ST and if its off substantially, I would put a long piece of pipe in the HT and a long 2X4 into the diamond of the frame and gently bend it.
Also, check the rest of the frame alignment using Sheldon Browns string method.
If it breaks, oh well, you were going to junk it anyway, right?
Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1