Ton any good mach shop be able to come up with an oversize guide it is an 8mm stem , but your first job get rid of those vlvs all of them , lay you 10 to 1 they are made in a place that start with the letter C and i don,t mean north of the border here,2 years ago i ordered 6 cyl heads at one time from a very large cyl head supplier whom i won,t name , got all the cyl heads and the vlvs to go with them the very first 3 i sent out, one broke an exhaust vlv in less than 300o miles , ask Curtis Johnson about this ones damage, the second one at 1500 miles was allready burnt on the exhaust , got hold of my customer who had the third head all ready installed and it was not running correct , sent him a new head only this time it had the factory vlvs in it the truck is still running , i immediately trashed canned all the rest of the vlv s and assembled the rest of the heads with the isuzu vlvs not one has been back , those vlvs from the "C" country cost 4.50 each, the ones from isuzu costs about 20.00 each, but they don,t burn and the heads don,t fall off, anyway when the guide broke did it tear up the head if not a stock guide should work fine ,anyway now you can get a brand new heavy wall casting , isuzu cyl head complete with all new vlvs, springs and cam shaft, all new rockers and rocker arms ready to bolt on completely assembled for right around 550.. freight paid in most places Jerry