Are you keeping the rear wheel or do you want to go for a 130mm road wheel? Depends on your plans for the bike and what level of groupset. Freebub cassette starts at 7 speed and 130mm. In general 126mm constrains you to 6 and 7 speed freewheel (although there are 126mm cassette hubs).

Since it is already 135 i would make it a straight 130 and make a wheelset around some road spaced 130mm hubs.