The J35D should be able to mount two 500 liter external drop tanks ( Probably XS version too but not sure )

[toyeLinux]

The J35A one external 530 liter drop tank

source:
Andersson, Lennart (2012). Fienden i öster, Svenskt jaktflyg under kalla kriget. Sweden (print, Bookwell Oy, Finland): Svenskt Militärhistoriskt Biliotek. pp. 105, 124. [ISBN] 978-91-86837-17-4