Tappets need adjusting every 6,000 miles anyway. In my case as I would do less than that in a year, so I'll just check and adjust once per year and do the engine oil and other bits at 6 month intervals. Tappets would also be affected if you have tightened or retorqued head bolts.
As it stands, I've been changing the oil, oil filter and coolant everytime I've started the engine recently with my ongoing head issues, but hopefully the end is now in sight.
Before mine broke, it was good for 55 by GPS. It could be pushed reluctantly to 60 but felt wrong at that speed. I felt if I attempted anything faster (or maintained 60 for any length of time), it would either explode or I would be left with permanent hearing impairment.
The handling is not exactly F1, so 50ish is probably a safe speed anyway and it's nice to be a spectator in a world of mental people rushing around.