Based on the data set name and variables names I think perhaps you should ask about this as a statistical analysis question not just as a data summary. Perhaps could look at your data give some advice.
However I will show you how you can use PROC ANOVA to compute the means differences as per your example. Using PROC ANOVA allows you do get the differences directly without having to do much in the way of data manipulation.
data crossoverdesign;
infile datalines delimiter=',';
input Id StdTyp Period Trtgrp @;
do d=1 to 3;
do r=1 to 3;
input sbp dbp @;
if sbp eq 999 then sbp=.;
if dbp eq 999 then dbp=.;
output;
end;
end;
datalines;
3,1,1,1,134,82,122,80,118,80,112,76,130,84,120,82,114,76,104,74,114,76
3,1,2,2,113,61,116,72,115,67,122,70,136,76,128,72,122,72,126,72,123,71
4,2,1,3,142,90,134,88,134,84,122,76,116,76,114,74,122,84,124,78,116,80
4,2,2,1,128,86,133,81,135,81,129,83,116,74,130,80,138,84,140,80,134,74
5,1,1,1,134,78,138,84,126,80,122,74,120,76,122,78,140,82,134,84,136,84
5,1,2,2,126,76,122,74,116,76,134,82,126,88,130,84,132,78,128,82,126,78
8,2,1,3,112,72,114,70,116,70,120,78,122,76,116,76,118,72,113,75,113,73
8,2,2,1,116,72,106,76,110,72,125,75,131,73,126,78,110,68,109,67,105,71
9,1,1,2,116,70,112,72,108,70,124,70,110,70,112,74,114,78,120,72,116,76
9,1,2,1,102,60,104,64,104,66,110,74,107,77,112,74,104,64,113,75,102,70
10,1,1,2,109,73,107,77,104,80,110,74,114,74,110,74,119,79,119,75,112,80
10,1,2,1,118,78,117,83,118,82,108,72,106,70,98,70,117,81,110,78,110,80
14,1,1,1,116,64,97,61,100,60,118,73,125,77,119,69,106,70,107,73,110,70
14,1,2,2,114,70,110,72,112,76,100,66,113,73,100,68,116,74,112,74,112,72
22,3,1,2,122,78,114,76,114,72,110,76,102,68,105,73,116,68,106,66,106,72
22,3,2,3,102,64,112,74,120,80,112,74,100,78,116,72,95,67,100,70,100,70
25,3,1,2,102,60,94,62,94,66,96,62,103,65,103,61,110,70,121,71,125,77
25,3,2,3,98,60,101,65,96,64,99,59,101,65,98,60,102,62,96,68,104,62
27,1,1,2,126,80,130,80,120,78,122,80,128,74,122,82,128,78,121,77,123,77
27,1,2,1,116,76,120,72,120,74,134,84,136,88,128,84,136,86,136,82,132,80
29,1,1,1,111,67,110,72,106,66,95,65,105,65,104,62,96,58,98,64,100,60
29,1,2,2,109,71,112,72,110,72,94,62,96,62,98,60,108,70,102,70,100,66
30,3,1,3,110,62,111,61,99,55,110,62,110,62,112,62,104,64,104,64,108,60
30,3,2,2,116,68,114,64,114,64,102,60,100,56,106,56,116,66,108,62,108,64
31,2,1,3,134,82,136,72,128,72,130,80,131,73,129,75,134,82,132,78,132,74
31,2,2,1,122,74,128,78,124,80,126,78,126,72,128,78,126,82,132,80,136,80
32,2,1,1,114,66,106,68,106,66,122,72,130,74,124,76,118,62,121,77,116,72
32,2,2,3,104,62,103,67,102,66,109,69,106,66,104,66,114,70,108,70,112,72
33,1,1,1,156,86,154,76,144,86,148,88,140,88,142,86,144,90,132,86,140,86
33,1,2,2,168,94,146,96,154,92,157,89,158,90,158,90,133,83,142,84,146,88
34,1,1,2,122,76,116,74,116,76,127,77,114,72,114,70,126,72,116,66,118,72
34,1,2,1,126,80,126,80,120,82,113,71,116,74,108,74,110,72,109,71,110,78
35,1,1,2,98,64,98,70,98,68,108,66,106,76,104,70,102,64,96,70,100,66
35,1,2,1,999,999,999,999,999,999,106,74,98,76,96,76,98,66,97,71,92,62
36,2,1,1,96,60,104,66,94,64,100,70,100,74,106,74,96,64,92,62,93,59
36,2,2,3,100,72,104,74,108,78,103,63,104,62,98,64,98,64,98,64,100,72
37,1,1,2,118,74,114,70,112,68,110,72,110,70,113,69,116,76,122,76,116,74
37,1,2,1,126,84,127,83,120,82,126,78,125,77,118,80,106,64,104,68,110,68
39,3,1,2,128,86,124,84,126,84,132,80,130,86,134,82,114,74,112,74,112,82
39,3,2,3,123,79,120,82,124,84,106,68,102,72,102,72,108,76,112,74,106,76
40,2,1,3,96,64,106,70,99,67,110,60,96,62,86,60,98,62,92,60,91,63
40,2,2,1,121,77,118,76,116,82,104,68,107,69,108,76,99,75,98,64,98,70
42,3,1,2,138,80,136,74,133,79,154,88,144,80,149,81,134,84,127,77,126,74
42,3,2,3,126,76,125,75,121,73,130,76,118,80,118,68,132,74,118,70,126,74
48,1,1,2,108,72,108,72,108,76,108,70,120,76,118,78,0,0,0,0,0,0
48,1,2,1,106,74,108,70,108,70,111,71,112,78,116,78,104,70,100,68,101,65
49,3,1,3,90,62,94,64,86,60,90,60,92,60,86,56,86,58,87,59,90,60
49,3,2,2,88,64,88,60,92,66,86,60,94,60,92,64,88,56,92,62,92,62
50,1,1,1,114,68,106,66,106,70,100,66,100,70,105,63,112,64,98,64,110,64
50,1,2,2,98,62,96,58,96,56,106,66,98,66,99,63,105,67,102,58,100,62
52,2,1,3,129,67,120,68,130,72,121,67,118,66,114,68,114,70,111,67,114,68
52,2,2,1,118,70,120,70,106,72,112,68,116,68,118,70,108,66,108,68,108,68
53,1,1,2,112,84,112,82,114,84,110,76,110,74,112,78,112,88,114,84,114,84
53,1,2,1,120,82,124,86,112,82,140,88,131,91,128,92,112,78,114,88,121,87
57,1,1,2,124,82,132,84,132,90,118,70,120,80,110,72,130,80,138,80,131,79
57,1,2,1,136,88,136,86,142,90,148,88,142,90,140,94,142,72,138,84,148,84
58,3,1,2,94,74,98,66,86,68,102,70,98,66,90,64,86,64,96,66,94,66
58,3,2,3,102,66,100,74,96,68,96,70,103,73,99,73,102,74,100,68,94,68
61,2,1,3,144,92,139,83,142,90,134,92,138,88,134,90,136,90,148,102,142,92
61,2,2,1,146,94,144,92,149,93,138,92,126,90,128,92,134,90,132,90,124,88
62,3,1,3,104,64,100,66,96,64,100,66,100,70,103,67,104,70,102,66,102,68
62,3,2,2,106,70,108,68,98,74,106,70,102,68,102,70,103,65,100,64,96,64
;;;;
run;
proc sort data=crossoverdesign;
by stdtyp period trtgrp;
run;
proc anova data=crossoverdesign;
by stdtyp period;
class trtgrp;
model sbp dbp = trtgrp;
means trtgrp / cldiff dunnett;
ods select none;
ods output CLDiffs=CLDiffs(drop=method uppercl lowercl significance);
run;
ods select all;
proc print data=CLDiffs;
run;