how to implement two megafunctions by serial?

i found another solution;

module ust_module(clock,a,b,result,overflow,underflow);
input clock;
input  a,b;
output  result;
output overflow,underflow; 
wire  c;
wire  d;
mult2 carpici2(
	.aclr(),
	.clk_en(1'b1),
	.clock(clock),
	.dataa(d),
	.datab(64'h4000000000000000),
	.denormal(),
	.indefinite(),
	.nan(),
	.overflow(overflow),
	.result(result),
	.underflow(underflow),
	.zero());
mult carpici(
	.aclr(),
	.clk_en(1'b1),
	.clock(clock),
	.dataa(c),
	.datab(64'h4000000000000000),
	.denormal(),
	.indefinite(),
	.nan(),
	.overflow(),
	.result(d),
	.underflow(),
	.zero());
	
adder  toplayici(
	.aclr(),
	.clk_en(1'b1),
	.clock(clock),
	.dataa(a),
	.datab(b),
	.denormal(),
	.indefinite(),
	.nan(),
	.overflow(),
	.result(c),
	.underflow(),
	.zero()) ;
	
endmodule

it works also

but there is another problem happens, i want to connect the result to input b but i want to add a d-flipflop on the line. or an shiftreg but these ffs are using 8 bits but my output bus is 64 bits. i want to use a mux-demux but i couldnt find any demux megafunction in quartus. Are there any option to change the bit selection in dff or shiftreg, or any demux example that i can use?