Being in a very restrictive retirement plan myself, I can understand the predicament.
If a stable value fund is available, I would put 30-50% in there, you will not break even with inflation but principle will be as safe as possible. And IMO the loss in purchasing power will be worth preserving principal; if you do not LOSE money then if and when a crash occurs you may be able to shift back into the market at much lower prices.
The rest I would split between large cap value, large cap growth and bond funds.
Everybody's plan is different, so without knowing your choices is is hard to say.
Some plans allow you to take a loan from it, depending on the terms of the loan it may be a good way to get some out of the system to deploy into metals/commodities, short funds, etc. In my plan one can take a loan for up to 50% of portfolio value, then the payment is taken right out of the paycheck, we pay 5.5% interest back into the plan, so you are ostensibly paying yourself interest. This is a non-taxable event.