You can't just drill the hole for the decomp shaft , it needs to be an accurate size and smooth finish to seal and line up inside . I have all the parts needed to do a kicker addition plus the decomp system but you need the cover machined , which I can do also but you'd need to send me your cover . If not in the states shipping would be too much though .

I think there is an aluminum plug that can be pulled out though . I've never tried it but I do think the bore is done once the plug is out . You can drill and tap it then used a slide hammer puller to get it out , maybe a little heat around the outer portion of the boss , just use care to not crack the end .