It will be a 1969 build if it has no ADR plate, probably late in 1969 by those numbers. If you want a 253, any 253H prefixed 253 is as wrong for the car as any other unless it is the original, so it won't really matter. The next best thing to the original would be a 253N prefix, cast anywhere from 1969 through to 1972-ish would be OK. I haven't actually seen a 253N but I have seen a few 308N (I have one in my shed), but the 253N engines will exist. Your best bet would be to just get any 253 (or 308 manual pattern for that matter) and dress it as a HT engine, so get HT-HG heads, HT rocker covers, air cleaner and timing case cover plus the alternator bracket. Although not absolutely correct a HQ intake will do. Finding a HT-HG water pump will be your biggest challenge. You can use HQ-WB engine mount adapter and mounts too, they are a better mount and do the same job.

Thanks for info, I was told it was an early build because of the location of the speedo cable hole but had know idea about that.