`x = 257, y = 917, rule = B3/S23`

10b2o71b2o77bo74bo$10b2o71b2o77bobo72bobo$162b2o73b2o$6bo149b2o67b2o4b

2o$6bobo141b2o4b2o67b2o4b2o$6b2o142b2o$2o169b2o73b2o$2o79bo89b2o73b2o$

81bobo$81b2o$75b2o$75b2o6$8b2o75b2o$8b2o75b2o57$13bo76bo75bo74bo$13bob

o74bobo73bobo72bobo$13b2o75b2o74b2o73b2o$7b2o75b2o74b2o73b2o$7b2o75b2o

64b2o8b2o73b2o$150b2o73b2o$2o20b2o51b2o22b2o74b2o48b2o23b2o$2o20b2o51b

2o22b2o74b2o73b2o68$17bo72bo77bo75bo$17bobo70bobo75bobo73bobo$17b2o56b

2o13b2o76b2o74b2o$11b2o62b2o7b2o64b2o10b2o74b2o$11b2o71b2o64b2o10b2o

61b2o11b2o$225b2o$26b2o71b2o76b2o74b2o$26b2o71b2o76b2o74b2o$2o$2o66$

19bo72bo76bo75bo$19bobo70bobo74bobo73bobo$19b2o54b2o15b2o75b2o74b2o$

13b2o60b2o9b2o75b2o74b2o$13b2o71b2o75b2o60b2o12b2o$225b2o$2o26b2o71b2o

75b2o74b2o$2o26b2o71b2o75b2o74b2o2$150b2o$150b2o65$20bo75bo73bo56b2o$

20bobo73bobo71bobo54b2o$20b2o74b2o72b2o$2o12b2o74b2o72b2o$2o12b2o74b2o

72b2o2$29b2o44b2o28b2o72b2o$29b2o44b2o28b2o72b2o50bo$231bobo$231b2o$

225b2o$150b2o73b2o$150b2o8$233b2o$233b2o54$12bo74bo75bo76bo$12bobo6b2o

64bobo6b2o52b2o11bobo6b2o51b2o13bobo6b2o$12b2o7b2o64b2o7b2o52b2o11b2o

7b2o51b2o13b2o7b2o$2o4b2o73b2o74b2o75b2o$2o4b2o67b2o4b2o74b2o75b2o$75b

2o70$16bo74bo73bo59b2o$16bobo6b2o64bobo6b2o63bobo6b2o49b2o15bo$2o14b2o

7b2o64b2o7b2o63b2o7b2o66bobo6b2o$2o8b2o63b2o8b2o72b2o81b2o7b2o$10b2o

63b2o8b2o72b2o75b2o$150b2o84b2o$150b2o69$18bo56b2o92bo74bo$18bobo6b2o

46b2o73b2o17bobo6b2o64bobo6b2o$18b2o7b2o65bo55b2o17b2o7b2o64b2o7b2o$

12b2o80bobo6b2o58b2o60b2o11b2o$2o10b2o80b2o7b2o58b2o60b2o11b2o$2o86b2o

$88b2o69$17bo77bo74bo75bo$17bobo6b2o67bobo6b2o64bobo6b2o44b2o19bobo6b

2o$17b2o7b2o67b2o7b2o64b2o7b2o44b2o19b2o7b2o$11b2o62b2o12b2o73b2o74b2o

$11b2o62b2o12b2o59b2o12b2o74b2o$2o148b2o$2o69$2o81b2o73b2o75b2o$2o81b

2o73b2o75b2o2$231bo$20bo210bobo$20bobo6b2o200b2o$20b2o7b2o50bo143b2o$

14b2o65bobo72bo68b2o$14b2o65b2o73bobo$75b2o79b2o$75b2o73b2o$150b2o6$

160b2o71b2o$160b2o71b2o2$77b2o$77b2o54$2b2o79b2o67b2o71b2o$2b2o79b2o

67b2o71b2o3$156bo$156bobo$81bo68b2o4b2o73bo$6bo74bobo66b2o79bobo$6bobo

72b2o142b2o4b2o$6b2o67b2o148b2o$2o73b2o$2o4$157b2o71b2o$157b2o71b2o4$

8b2o67b2o$8b2o67b2o54$7b2o66b2o78b2o70b2o$7b2o66b2o9bo68b2o70b2o$86bob

o$80b2o4b2o$80b2o74bo74bo$90b2o64bobo72bobo$6bo83b2o58b2o4b2o67b2o4b2o

$6bobo141b2o73b2o$2o4b2o$2o6$2b2o146b2o80b2o$2b2o146b2o80b2o59$7b2o71b

2o68b2o73b2o$7b2o71b2o68b2o9bo63b2o$161bobo$155b2o4b2o$81bo73b2o$81bob

o81b2o$6bo68b2o4b2o82b2o64bo$6bobo66b2o154bobo$2o4b2o217b2o4b2o$2o223b

2o6$2b2o71b2o153b2o$2b2o71b2o153b2o!

A large number of reactions is based on these G+2 blocks->2G+B-heptomino reactions and they differ only in the way how the last block collides with B-heptomino and destroys it:

`x = 67, y = 30, rule = B3/S23`

12$48bo$48bobo$48b2o$14bo27b2o$14bobo6b2o17b2o$14b2o7b2o$8b2o47b2o$8b

2o47b2o!

Since B-heptomino may react with another block to produce a glider, there is a positive answer to your G+3 blocks->3G question:

`x = 33, y = 11, rule = B3/S23`

22bo$22bobo$22b2o$16b2o$16b2o2$31b2o$31b2o2$2o$2o!

EDIT: Actually they are already listed in knightlife's post here: viewtopic.php?f=2&t=1065

EDIT: These two are interesting because they send gliders onto the same track:

`x = 60, y = 23, rule = LifeHistory`

2.2A$2.2A54.2A$58.2A5$6.A49.A$6.A.A47.A.A$6.2A48.2A$2A48.2A$2A48.2A9$

8.2A$8.2A42.2A$52.2A!