[Tom Goldman]

Seats,front and rear ,wiring harness, sound deadener , factory carpets ,all the unnecessary underdash stuff ,} defroster ducts and dash controls must stay }are the biggest gain for the least expense.
Door guard beams are also good for quite a bit of weight .
Aluminum bolts and screws on non suspension parts can reduce as much as 15 - 20 # on big cars. using the shortest bolts possible elsewhere all adds up.
Getting rid of the factory fuel tank in favor of a 3 gallon cell and pump is a big weight loss, but will take several hundred bucks from the budget. .
On the more pricy side are the lithium batteries ,but the weight savings are huge and when getting to the last 30-40 # is necessary an expense that may need to be taken.
I've had very good results using batteries from Antigravity Battery .
You mentioned adjustable seats , unless drastically different size drivers are going to be running the car, a waste of both money and weight .
Some modern steering wheels are are very heavy to dampen vibration, and to frevent breakage during airbag deployment .
Ive found light wheels that weigh as little as 1 3/4 pounds [Stock car stuff]