If you were to use a Comp beehive spring in that application, it would work fine. Hyd lifters are really not meant for high rpm, so if you kept it below 6000 rpm or right around the 6000 rpm limit then you should be fine. What happens with the bigger cam, is you need springs that can handle the cam and that places a strain on the stock sized bolts. Using the beehives, you can gain control without having to use excessive spring pressure which should work well up to or around 6000 rpm. That's what I would do cause $300 is too much for that little machining.
The conversion guide plates and studs are fine if you keep the spring persure way down . You have to remember that cleveland 4V valves are heavy and they need stif springs to controle there weight . If you run to week of a spring and drop a valve it will do a lot more damage than what the machine work would cost . The 5/16 ends on the screw in studs are not heavy enough to handle a lot of stress.