A whole gaggle of places turn up now in Dorset, including the front gate to Thomas Hardy's home, Max Gate, in Dorchester, where Reed paid a call on Hardy's widow in the autumn of 1936, while he was still hoping to produce a biography of his hero. Then, we arrive outside Yetminster's stately, 17th-century Gable Court, where Reed spent a very productive year between 1949 and 1950, until he moved to London. It was while at Gable Court (currently listed as "Milford House" at British Listed Buildings online, but the sign on the gate clearly still says "Gable Court," today) that Reed wrote his radio dramas based on the life of the Italian poet and philosopher, Giacomo Leopardi: The Unblest (first broadcast May 9, 1949), and The Monument (March 7, 1950).
Best of all, Google Street View actually helped me resolve a minor detail: the exact location of Lovell's Farm (click the minus "-" sign to zoom out) in Marnhull, which I simply could not seem to place.
Reed, accompanied by Michael Ramsbotham, rented this ample farmhouse after World War II, from as early as August or September, 1946, until possibly as late as their move to Gable Court, in early 1949. There, according to Jon Stallworthy's introduction to the Collected Poems, while Ramsbotham worked on a novel (perhaps The Parish of Long Trister), Henry Reed researched his never-completed Hardy biography, wrote book reviews for The Listener, and occasionally traveled to London to give literary and literate talks on the BBC's Third Programme. His first full-length play for the BBC, a radio adaptation of Moby Dick, was most likely completed at Lovell's Farm, being broadcast on January 26, 1947. When the play was published later that year, Reed's Preface was signed from Marnhull.
I never would have found the farm, but for the detailed description in An Inventory of Historical Monuments in the County of Dorset (1970), which allowed me to pinpoint it in Google Maps' aerial view. Even in dry, planed-and-sanded language, the house sounds absolutely heavenly:
LOVELL'S FARM (77511938), 1,000 yds. N.W. of the church [St. Gregory's], is of two storeys with dormer-windowed attics; it has walls of coursed rubble with ashlar dressings, and roofs of tiles and stone-slates. The S. range has a symmetrical S. front and is probably of the 17th century. It was extended to the E. in the 18th century and a wing was built northwards from the E. end of the extension early in the 19th century. The original part of the S. front has a rubble plinth and is of two bays with a central doorway; above the ground-floor window heads is a continuous weathered and hollow-chamfered string-course. The windows of both storeys are of three square-headed lights with recessed and beaded stone architraves and beaded mullions; the doorway surround is similar, with the addition of a fluted keystone. Over the doorway is a segmental wooden hood with a dentilled cornice and shaped brackets. The E. extension has neither plinth nor string and the window surrounds are of wood. The N. wing is of roughly coursed rubble, with tiled roofs with stone-slate verges; the windows are of wood. Projecting N. from the W. part of the original S. range is a gabled N.W. wing. It has wood-framed windows with 18th-century leaded iron casements on the ground and first floors; the attic window has modern casements; all these openings are spanned by long timber lintels. In the E. wall is a small circular first-floor window with a recessed ashlar surround and radial leaded glazing.
Inside, the room at the W. end of the original range has 18th-century fielded panelling, in two heights, with moulded dado rails and cornices. In a cupboard beside the 18th-century fireplace are preserved the chamfered stone jamb and continuous wooden bressummer of an open fireplace. S. of the fireplace is an external doorway, now blocked up and used as a cupboard. The partition between this room and the entrance vestibule is of plank-and-muntin construction with beaded edges. Several ground-floor rooms have deeply chamfered ceiling beams. A window pane has a scratching of 1738.
Inside, the room at the W. end of the original range has 18th-century fielded panelling, in two heights, with moulded dado rails and cornices. In a cupboard beside the 18th-century fireplace are preserved the chamfered stone jamb and continuous wooden bressummer of an open fireplace. S. of the fireplace is an external doorway, now blocked up and used as a cupboard. The partition between this room and the entrance vestibule is of plank-and-muntin construction with beaded edges. Several ground-floor rooms have deeply chamfered ceiling beams. A window pane has a scratching of 1738.
(v. 3, Pt. 2, "Central Dorset," p. 158)
After all my virtual driving around Marnhull, grinding gears going forwards and reversing, confirming the location was as simple as another search in British Listed Buildings. I've also gathered some screenshots taken in Street View into a Flickr set.