As long as you are dilligent in changing the oil, any "normal" oil will work just fine. Synthetics are good oils but they do not "agree" with everything.
The main advantage with syns is that they are formulated to withstand very high oil temps, and they do.
After the Mobil 1 fiasco (Cadillac vs. Mobil Oil - Cadillac's faulty engine but Mobil paid for them), 20 years ago, none of the oil manufacturers and distributors will tell you to ignore the engine manufacturers recomendations.
One of our trucks is a GMC HD with a 454 gas. It has 200+ on it and never had a problem. It gets 7 qts of synthetic, Mobil or Castrol, whatever is available EVERY 10,000 - 12,000 miles. The truck does 200-300 miles per day and taking it in for an oil change once a week is almost impossible (We do not use quick lubes). Still purrs like a kitten.
On the other hand, we also have International diesels (T444E) that we only use 15-40. 5 gallons (not qts) of synthetic gets expensive. A couple have more miles than the GMC.
My suggestion is to try it. Watch for leaks (synthetic is fussy about seals). If you do not see any leaks after the engine has run for some time, you are okay. If in doubt, just use a high grade oil SAE-SH rated motor oil and you still will be okay.
I hope this helps.