If only RemFlex was SlimFlex

We must apologize for not going to Remflex website and researching what parts they sell so we understand your question (easier for you than just telling us).

Yes, you could get longer studs. They are pretty standard. Ace Hardware carries some in the pull-out drawers. But, I wouldn't since likely to break one off trying to remove from the head, and that would cause bigger issues. Better to just get it started without washers, as recommended.

Also, keep the 3 vertical bolts that clamp the intake and exhaust snug but loose while you snug up the nuts to the head, keep repeating back and forth so everything settles in correctly. I coat those 3 bolts w/ high-temp anti-seize to avoid the common "snapped middle bolt" on the next removal.

Before doing anything, read the excellent article on slantsix.org. The cone and triangle washers are supposed to face opposite what "common sense" suggests. If you don't, the exhaust manifold can later crack.